Symptoms

Specific userA is having trouble starting IM conversations with users very sporadically. If userA tries to initiate a chat with a user they get back an error "The following Message was not Delivered to userB" UserB who userA tries to send to can initiate a conversation back to userA and then they can chat fine. The next day, userA may be able to chat with userB fine but not other users.....seems very sporadic and random in nature. It happens to the userA regardless of computer he is on and seems to be happening regularly with people he tried to chat with.
When performing a search in MOC for userA, userA comes back twice, first as a group and second a contact.

Cause

An email address was assigned to a security groups email attribute that matched userA's SIP URI. As a result, the OCS Address Book service picked that up and created a group in the Communicator address book.

Resolution

The fix was to remove the SIP URI of userA from the security groups email attribute and update the OCS Address book by allowing for replication.

More Information

Communicator ETL event from userA
TRACE_LEVEL_ERROR [1]0DB0.196C::03/29/2010-14:52:59.288 (CConversationUtil::GetContactModelBySipUri:ConvUtil_cpp3614)0x00000000HRESULT failed=0x80070057(ERROR_INVALID_PARAMETER)