Lots of other threads about similar issues, but none that I could find where quite the same case as mine. So, here goes:
Things I did:
Try to uninstall your virtualenv and virtualenvwrapper and install it again using pip (check if you symlink your pip or assigned an alias on it for other version) in version 2.7 (I think).
I encountered the same error and I just did this and solved my problem.
I using Ubuntu machine.
I hope this help.