Creating a new Account

For some odd reason i can create a new account just, but when i try to log in the screen just shakes, i've tried with and without a password

I've also tried renaming an old account which previously logged in ok, only to get the same shaking screen

I'm sure i read somewhere about a conflict with a program called Growl, whether this is true or not, i cannot find any association with Growl on the HDD

Any suggestions?

Only time mine has done that is when I entered the wrong password. Are you sure you have the correct password?