Comment 25 for bug 136529

For me 2 solutions worked:

solution 1 (simple):
from failsafe session create new user - this new user will work perfectly

solution 2:
from terminal (Ctrl-Alt-f2 for instance) _move_ all configuration to new directory:
sth. like
mkdir invalid_conf
mv .* invalid_conf
then check (login/logout gnome session) your old account - it should work now,
then
- move half of remaining 'invalid' configuration to your home
  (eventually after login error move back half of last portion of files to invalids)
- check account (login/logout gnome session)
- rinse, repeat
this way you will find invalid configuration file, which you can throw away or repair

for me it was invalid entry in .profile which I have add myself before :-)