ruby on rails 4 - heroku precompiling asserts failed: Sass::SyntaxError: Undefined variable -

i develop app based on m. hartls tutorial. when try push sample-app on heroku, precomiling of assets fails error:

sass::syntaxerror: undefined variable: "$gray-lighter"

in none of files mention "gray-lighter". application.css.scss contains only:

/*  *= require_tree .  *= require_self  */ @import "bootstrap-sprockets"; @import "bootstrap"; 

has idea how solve problem? besides error code - need more information?

$ git push heroku master -f counting objects: 168, done. delta compression using 2 threads. compressing objects: 100% (154/154), done. writing objects: 100% (168/168), 40.30 kib | 0 bytes/s, done. total 168 (delta 32), reused 0 (delta 0) remote: compressing source files... done. remote: building source: remote: remote: -----> ruby app detected remote: -----> compiling ruby/rails remote: -----> using ruby version: ruby-2.2.4 remote: ###### warning: remote:        removing `gemfile.lock` because generated on windows. remote:        bundler full resolve native gems handled properly. remote:        may result in unexpected gem versions being used in app. remote:        in rare occasions bundler may not able resolve dependencies @ all. remote:        https://devcenter.heroku.com/articles/bundler-windows-gemfile remote: remote: -----> installing dependencies using bundler 1.9.7 remote:        running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 remote:        fetching gem metadata https://rubygems.org/........... remote:        fetching version metadata https://rubygems.org/... remote:        fetching dependency metadata https://rubygems.org/.. remote:        resolving dependencies.... remote:        installing i18n 0.7.0 remote:        installing rake 10.5.0 remote:        installing minitest 5.8.4 remote:        installing thread_safe 0.3.5 remote:        installing builder 3.2.2 remote:        installing erubis 2.7.0 remote:        installing mini_portile2 2.0.0 remote:        installing rack 1.6.4 remote:        installing json 1.8.3 remote:        installing mime-types 2.99 remote:        installing arel 6.0.3 remote:        installing execjs 2.6.0 remote:        using bundler 1.9.7 remote:        installing coffee-script-source 1.10.0 remote:        installing sass 3.4.21 remote:        installing thor 0.19.1 remote:        installing concurrent-ruby 1.0.0 remote:        installing multi_json 1.11.2 remote:        installing bcrypt 3.1.10 remote:        installing libv8 3.16.14.13 remote:        installing rails_serve_static_assets 0.0.5 remote:        installing rails_stdout_logging 0.0.4 remote:        installing ref 2.0.0 remote:        installing tilt 2.0.2 remote:        installing tzinfo 1.2.2 remote:        installing rack-test 0.6.3 remote:        installing pg 0.17.1 remote:        installing mail 2.6.3 remote:        installing autoprefixer-rails 6.3.1 remote:        installing puma 2.11.1 remote:        installing uglifier 2.7.2 remote:        installing coffee-script 2.4.1 remote:        installing bootstrap-sass 3.2.0.2 remote:        installing sprockets 3.5.2 remote:        installing rails_12factor 0.0.2 remote:        installing activesupport 4.2.5 remote:        installing rails-deprecated_sanitizer 1.0.3 remote:        installing globalid 0.3.6 remote:        installing activemodel 4.2.5 remote:        installing jbuilder 2.4.0 remote:        installing activejob 4.2.5 remote:        installing activerecord 4.2.5 remote:        installing nokogiri 1.6.7.2 remote:        installing rails-dom-testing 1.0.7 remote:        installing loofah 2.0.3 remote:        installing rails-html-sanitizer 1.0.3 remote:        installing actionview 4.2.5 remote:        installing actionpack 4.2.5 remote:        installing actionmailer 4.2.5 remote:        installing railties 4.2.5 remote:        installing coffee-rails 4.1.1 remote:        installing sprockets-rails 3.0.1 remote:        installing jquery-rails 4.1.0 remote:        installing turbolinks 2.5.3 remote:        installing rails 4.2.5 remote:        installing sass-rails 5.0.4 remote:        installing therubyracer 0.12.2 remote:        bundle complete! 23 gemfile dependencies, 57 gems installed. remote:        gems in groups development , test not installed. remote:        bundled gems installed ./vendor/bundle. remote:        bundle completed (33.06s) remote:        cleaning bundler cache. remote: -----> preparing app rails asset pipeline remote:        running: rake assets:precompile remote:        i, [2016-02-05t18:12:00.582969 #1174]  info -- : writing /tmp/build_f90401fc14a7fa141740de8ac82224af/public/assets/application-5caa7ce0a1e3d41955b9f91ccab3418d4f098eee350d3d8dcd9698c5fe32ca66.js remote:        i, [2016-02-05t18:12:00.583759 #1174]  info -- : writing /tmp/build_f90401fc14a7fa141740de8ac82224af/public/assets/application-5caa7ce0a1e3d41955b9f91ccab3418d4f098eee350d3d8dcd9698c5fe32ca66.js.gz remote:        rake aborted! remote:        sass::syntaxerror: undefined variable: "$gray-lighter". remote:        (sass):73 remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/script/tree/variable.rb:49:in `_perform' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/script/tree/node.rb:50:in `perform' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/script/tree/list_literal.rb:63:in `block in _perform' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/script/tree/list_literal.rb:63:in `map' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/script/tree/list_literal.rb:63:in `_perform' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/script/tree/node.rb:50:in `perform' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:395:in `visit_prop' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/base.rb:36:in `visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:158:in `block in visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/stack.rb:79:in `block in with_base' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/stack.rb:115:in `with_frame' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/stack.rb:79:in `with_base' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:158:in `visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:431:in `block (2 levels) in visit_rule' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:431:in `map' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:431:in `block in visit_rule' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:179:in `with_environment' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:429:in `visit_rule' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/base.rb:36:in `visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:158:in `block in visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/stack.rb:79:in `block in with_base' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/stack.rb:115:in `with_frame' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/stack.rb:79:in `with_base' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:158:in `visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:431:in `block (2 levels) in visit_rule' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:431:in `map' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:431:in `block in visit_rule' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:179:in `with_environment' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:429:in `visit_rule' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/base.rb:36:in `visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:158:in `block in visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/stack.rb:79:in `block in with_base' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/stack.rb:115:in `with_frame' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/stack.rb:79:in `with_base' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:158:in `visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/base.rb:52:in `block in visit_children' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/base.rb:52:in `map' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/base.rb:52:in `visit_children' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:167:in `block in visit_children' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:179:in `with_environment' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:166:in `visit_children' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/base.rb:36:in `block in visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:186:in `visit_root' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/base.rb:36:in `visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:157:in `visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/visitors/perform.rb:8:in `visit' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/root_node.rb:36:in `css_tree' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/tree/root_node.rb:20:in `render' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sass-3.4.21/lib/sass/engine.rb:278:in `render' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/sass_compressor.rb:48:in `call' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/sass_compressor.rb:28:in `call' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/processor_utils.rb:75:in `call_processor' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/processor_utils.rb:57:in `block in call_processors' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/processor_utils.rb:56:in `reverse_each' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/processor_utils.rb:56:in `call_processors' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/loader.rb:134:in `load_from_unloaded' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/loader.rb:60:in `block in load' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/loader.rb:318:in `fetch_asset_from_dependency_cache' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/loader.rb:44:in `load' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/cached_environment.rb:20:in `block in initialize' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/cached_environment.rb:47:in `yield' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/cached_environment.rb:47:in `load' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/base.rb:66:in `find_asset' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/base.rb:73:in `find_all_linked_assets' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/manifest.rb:142:in `block in find' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/legacy.rb:114:in `block (2 levels) in logical_paths' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/path_utils.rb:225:in `block in stat_tree' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/path_utils.rb:209:in `block in stat_directory' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/path_utils.rb:206:in `each' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/path_utils.rb:206:in `stat_directory' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/path_utils.rb:224:in `stat_tree' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/legacy.rb:105:in `each' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/legacy.rb:105:in `block in logical_paths' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/legacy.rb:104:in `each' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/legacy.rb:104:in `logical_paths' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/manifest.rb:140:in `find' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/sprockets/manifest.rb:168:in `compile' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-rails-3.0.1/lib/sprockets/rails/task.rb:68:in `block (3 levels) in define' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-3.5.2/lib/rake/sprocketstask.rb:147:in `with_logger' remote:        /tmp/build_f90401fc14a7fa141740de8ac82224af/vendor/bundle/ruby/2.2.0/gems/sprockets-rails-3.0.1/lib/sprockets/rails/task.rb:67:in `block (2 levels) in define' remote:        tasks: top => assets:precompile remote:        (see full trace running task --trace) remote:  ! remote:  !     precompiling assets failed. remote:  ! remote: remote:  !     push rejected, failed compile ruby app remote: remote: verifying deploy... remote: remote: !       push rejected myapp-30998. remote: https://git.heroku.com/myapp-30998.git  ! [remote rejected] master -> master (pre-receive hook declined) error: failed push refs 'https://git.heroku.com/myapp-30998.git'