Users can't login after upgrading

I have just upgrading the ladder at http://games-ladder.net/Mmentorentor. I ( the admin) successfuly can login and see my options but the other users have a problem.

I have got this info fom them all:

"I logged in with the new password, but it doesn't seem to recognize that I'm logged on, because I cannot challenge anyone, or change my password. It says at the top of the randkings page that I'm logged on, but at the bottom of the page it still says "please note that you have to be logged in to see the full list and access the challenge functions."

Please advice ...