Could not find required OpenGL entry point 'glGetError'
Solution 1:
I found the solution to my problem. To get TF2 to work again all I had to do was remove the symbolic link that I made to get Skype working:
/usr/lib/i386-linux-gnu/mesa/libGL.so.1
The problem now is Skype doesn't work again. I guess I'll just have to remake the symbolic link whenever I want to use Skype until Canonical fixes the seg fault issue with Skype.
Solution 2:
I know this is an old thread but removing / deleting this symlink is not a great answer at all. Many other applications depend on this file, although steam requires current drivers.
Please read my solution to this issue:
Ubuntu 14.04 “could not find required OpenGL entry point 'glGetError'!"