Connection problems

[Tim]

We have a windows 2000 terminal server, our users are a mix of dumb
terminals and MS rdp client running on win2000 and XP.

For the past month or so the clients are being disconnected from the server,
the only error message is one that say "due to a data encryption error this
session has been disconnected. Please try and login again"

If the user is on a PC then 99% of the time they can log back in to the same
place they were working. Those on dumb terminals are not always so lucky,
sometime they lock up completely and when they do log back in they find
that they have lost there work (a fresh login).

There is nothing reported in any of the event logs in fact we don't see any
evidence of the problem on the server only the users see the problem.

Anybody any suggestions??

Tim