10.4 Clients hang on log on windows

Hi, I hope somebody can help me. I'm stumped!!! All of our 10.4 clients are able to log in once to our AFP server, but if you do a log out and attempt to log in as another user, the log on windows greys out and the computer hangs. The only way to get back is to do a hard reset of the computer and then users are able to log in. Our 10.3.9 Macs do not have this problem logging in to the server, and we just received a shipment of 20" Intel iMacs, straight out of the box, I set up appropriate settings in Directory Access, and they do the same problem. We are authenticating to a G5 xserver running Mac OS X 10.4.8 Server. Last year we were running 10.3.9 and the client machines had no problem logging in. I hope somebody can help with this!