Communicator Login Problems

Throught my time working with Microsoft Communicator 2005 I've had a number of issues - some realtively easy to fix, some creating errors that even Microsoft don't have a solution for. It you get any of the following errors, try these solutions:

1. Can't login to Comunicator - I've had this problem whereby a user authenticating on to domain, on a computer which is not actually a member of that domain, cannot login periodically. No connectivity problems, no firewalls in the way, just would not log in.

The way I found to fix it was to logout of Communicator and navigate to the following registry key:

[HKEY_CURRENT_USER\Software\Microsoft\Communicator]

Navigate to the key called:

"UserMicrosoft RTC Instant Messaging"=" "

now, delete the domain\username part of the key.

I know what you're thinking - it asks me for this anyway, so why bother deleting this part of the key? That I can't answer - apart from guessing that the security token becomes invalid after a certain amout of time possibly, but either way this works for me on that certain computer ever time i get a login error.

Hope that helps somebody out there...