I had the same issue with 11.10, but you did not.
Eve worse, with 12.04. I'd enter the password, it would do nothing after pressing enter.
The only way round this was to alt+F2 to another terminal, log in via text, sudo service lightdm restart, then login via graphical method. Then wash, rinse, repeat 2-3 times. Eventually getting a desktop.
Updating to nvidia-post-release updates fixed this.....sort of. Now I'm back to having to enter my password twice at the lightdm login, but at least its consistent in letting me login on the 2nd attempt each time, without having to restart the lightdm service.
Sorry, no solutions from me to your issue.
I think, therefore I compile