The following event is logged in the Lync Server log on a Microsoft Lync Server 2010 Group Chat server:
Log Name: Lync Server Source: LS MGC ENDPOINT Logged: Date Event ID: 5377 Task Category: (1099) Level: Error Keywords: Classic User: N/A Computer: Computer Name Description: Failed to update the database with AD changes.  String or binary data would be truncated. The statement has been terminated.
This issue occurs if you create a user in Active Directory Domain Services whose distinguished name contains more than 256 characters, and then you add this user to a distribution group.
To resolve this issue, install the following cumulative update:
2514984 Description of the cumulative update for Lync Server 2010, Group Chat: November 2011
Note After you apply this update, the Group Chat server supports users whose distinguished names contain up to 384 characters.