Exchange Messenger not updating

[Stuartp]

We use the Exchange Messenger facility under Exchange 2000. Until recently all was well, then a few days ago the contact lists stopped updating. Users are not notified when new users sign in and if a user goes away this is not reflected on all the other lists. The only way to update the list is to sign out and in again.

There have been no firewall changes so it isn't that. I have tried deleting and recreating the Instant Messaging Virtual Server under Exchange Manager and reassigning all the users to it, and I have also gone through all the steps of this MS knowledge base article:

http://support.microsoft.com/default.aspx?scid=kb;en-us;283689

all to no avail.

Has anyone else had this problem and solved it and if so please can you tell me how!

Thanks

Stuart