I've been pulling my hair out trying to solve this problem and I've tried everything and I have no ideas left.
I keep seeing this error: Exception Value: 'thumbnail' is not a valid tag library: Could not load template library from django.templatetags.thumbnail, No module named sorl.thumbnail.main
$DJANGO_PACKAGES/sorl/thumbnail/main.py DOES exist.
Here's what I did to setup,
downloaded latest sorl-thumbnail and added its location to the python path in .bash_profile
included 'sorl.thumbnail' in INSTALLED_APPS (in django's settings.py)
used the {% load thumbnail %} tag in a django template
It would seem obvious sorl-thumbnail is not installed correctly, but I'm able to import thumbnail from the python shell and the django shell (when I use {% load thumbnail %} it brings this error). Also, there are no typos in related files (I've checked many many times).