Workgroup Member Can’t Logon

Two Win2K machines in workgroup. Same user names and same passwords in both. Users part of Administrators group on both machines. Prior to last week, PC A could access PC B with no problem. Somebody switched something.

When trying to connect fromPC A to PC B, we get “\\PC B not accessible. Logon Failure: the user has not been granted the requested logon type at the computer.”

Drive shared to everyone-Full Access (stupid I know). NTFS set to Everyone Full Access. PC A can see PC B and vice versa. PC B can access PC A with no problem. Both can access the Internet OK. PC A can ping PC B.

What could they have done to screw up a workgroup like this?

HELP!