Others showing Offline on Messenger 5.1 through SIP with LCS 2005

Hi all, I have an LCS 2005 Server that is running SIP communications in our office for about 20 users over TCP connections.  All of the users are using Windows Messenger 5.1 for connectivity to the LCS.

Everything was working just fine on it until the middle of last week, when I added a user with Messenger on Mac (our first one) to the fold.  The user on the Mac was connects in just fine to the LCS.  However, ever since he has started using LCS and Messenger on Mac, many users, myself included are finding that we can sign-in just fine to the LCS, but all of our contacts show as offline and are showing their full SIP addresses, not the shortened names they usually show when they are online.  Also, if we attempt to initiate a conversation with a user, it simply opens up a new e-mail within Outlook.  However, the users that are lucky enough not to be affected can see myself and the other affected users online just fine, and they can initiate messaging with us, and once they do, we can carry SIP communications back and forth, as long as we keep the conversation window open.

What's even stranger is that, there is no common thread (that I can tell) between those that have the problems, and those that do not.  I've tried reinstalling Messenger, I've tried restarting both services and the Server that hosts our LCS SIP service, to no avail.  

Any help on this would be GREATLY appreciated.  Thanks!
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I had this problem at a company that I used to sysadmin for, except it was with Outlook Messenger and intranet users not showing up on contacts. What worked for me was changing the IP scope in the effected users' programs settings to only scan the IP's in our domain (i.e. -  Also adding the names/contacts to the safe senders/trusted contacts/etc list also in the settings.  Slightly different program but maybe that will lead to some clues.
Have you tried turning it off and then on again?
CMICITAuthor Commented:
Hi Tymetwister, there really isn't a place to specify IP ranges for end-users with Windows Messenger, at least, not that I've found.  I can specify the server to connect to either by IP or FQDN.  I've tried changing both, but neither one has made any difference.

And Corvus, yes, I've tried turning off the Server and turning it back on, along with the services individually.  I have also tried restarting the clients affected as well, but I have not had any success.

One weird thing I have found, if I try to search for a user to add by clicking the "add contact" link on messenger, it will find users within my organization just fine, but it says that the user cannot be found when I actually try to finish the add contact wizard.

Any other ideas?

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CMICITAuthor Commented:
We ended up turning off SIP and completely rebuilding the server.  That fixed the issue.
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