First make sure you have checked the most voted answer.
I’m not sure if it’s exactly your problem, but in my case, I wasn’t able to upgrade Django to 1.2.4 – I was always finishing with 1.2.3 version, so I uninstalled Django with:
<virtualenv>/bin/pip uninstall Django
Then I removed
<virtualenv>/build/Django directory and finally I installed the proper version with:
<virtualenv>/bin/pip install Django