apache - 500 Error when trying to pass Python object to HTML using Flask/mod

i've got flask application running on top of apache using mod_wsgi. i'm trying pass object i've created template this:

@app.route('/<user>') def viewuser(user):     return render_template('viewuser.html', user = builduser(user))

where builduser returns instance of class 'user' based on username.

viewuser.html accesses of fields of 'user' this:

hello, {{ user.name }}!

this runs fine on local flask server, browser returning '500 internal server error' when try access http://myurl.com/testuser.

templates otherwise working fine - example if change view function return value to:

return render_template('test.html', user = user)

and test.html contains:

hello, {{ user }}!

everything displays correctly. (http://myurl.com/testuser displays 'hello, testuser!')

does have idea why passing simple values works on apache mod_wsgi, passing objects works on non-production flask server?

Ben