The following are the possible causes for this problem:
The server cannot validate the session token.
Instant Messaging channel is not configured properly. For example, incorrect Instant Messaging server host, port, or both.
Plug-in or Java Web Start is not installed or is not functional.
End user not found and the Instant Messaging server cannot find the end user when performing an LDAP lookup.
Where to get diagnostic information:
Instant Messaging server and Instant Messaging channel logs.