Sign-in Failure

[Andrew Prior2]

HPSIM 5.2 on Windows 2003 server

Getting the message 'Sign-in Failure' when anyone attempts to log on.

HPSIM was working perfectly ok up until a couple of days ago, now it is not possible to log on to the console either on the server itself, or from a webpage elsewhere.
This applies to all accounts that previously had permissions.
HPSIM has a local database.

All services (which run under a local account taht is in the local administrators group) are started. No accounts are locked out.
no changes have been made that I'm eiterh aware of or can see.

Anyone have any ideas on what might be at fault, what can be checked and any workarounds (if any).