If you are on ubuntu and you get this bug, this might be because the python that you were using in a virtualenv was updated. ubuntu and some other distros may do this automatically.
You can verify that this occurred by looking at the:
or log in the equivalent location on your system.
The quick fix is to just re-run virtualenv.
In my case this was as simple as:
$ virtualenv .
I hope this helps some people out there.