Migration assistant (PC to Mac) - cannot open new user account

I have done the following:

- upgraded to lion

- used the migration assistant to move data from my old PC to the mac

- transfer worked fine

but now, on the mac, I cannot open the new (automatically created) user account

Note: I did not have a password on the old pc

What I tried so far is to change the password of the new created user account in the utilities section but when I want to sign in (chaning user by clicking on the current user in the top right) it does not accept the new password. In addition when I log out of teh current user account, and try to log into the new one, I get a pop up window that asks me to reset the password. So I type in a new password and confirm it but it does not accept it (the pop up window does not close but refuses my input so I have to cancel)?

Anybody has any idea what the problem is or what I could try?

Thank you!