Directory services error in Event log

We are running a mixed mode win2k network and one of our win2k server, the proxy server, is now not allowing anyone to access it via a share or for backup. Investigating the event logs shows a Directory Servcie error of:

Error 6(6) has occurred (internal Error 321058c)Please contact Microsoft Product support services.

As well as this, the server has disappeared from Active Directory Users and Computers to be replaced by the details of what it was called when it was a NT4 server 9 months ago.

I have also noticed that in the AD it looks as if people have been adding Domain controllers and then just diconnecting them leaving the entries in the AD.

Any sensible ideas / suggestions greatly appreciated.