cannot copy files, object name no longer available

Since a few days ago when I completed a migration from NT to Windows 2003
and removed all traces of NT going into Win 2003 native mode, there are a
few computers that cannot copy big files from the fileserver on the network.

After some random time trying to copy, where I can see there are packets
going back and forth, the error message is:

Cannot Copy [filename]. The specified network name is no longer available.

After some research, there are two elements that may contribute to the
problem:

a) The fileserver is also a DC, and
b) The problem only presents itself in Client PCs using Windows 2000
Professional, WITH ALL UPDATES INSTALLED. Win 2K client computers without
the very LATEST patches work fine, as do Win XP client computers.


All windows 2000 Professional computers have version 5.00.2195 with SP4.
Coputes with up to pach KB842526 work well.

There a re no error in the logs of either the client workstation, nor the DC
or fileservar computers.

Thanks in advance,

Maje