Article ID: 968624
When you disconnect a computer that is running Microsoft Office Communicator 2007 R2 from the network, the following events may be logged in the Application log:
Log Name: Application Source: Communicator Event ID: 3 Task Category: None Level: Error Keywords: Classic User: N/A Description: Communicator was unable to resolve the DNS hostname of the login server OCS_Server_FQDN. Resolution: If you are using manual configuration for Communicator, please check that the server name is typed correctly and in full. If you are using automatic configuration, the network administrator will need to double-check the DNS A record configuration for OCS_Server_FQDN because it could not be resolved.
Log Name: Application Source: Communicator Event ID: 7 Task Category: None Level: Error Keywords: Classic User: N/A Computer: <Client_machine_FQDN> Description: Communicator failed to connect to server OCS_Server_FQDN (IP_address) on port 5061 due to error 10061. The server is not listening on the port in question, the service is not running on this machine, the service is not responsive, or network connectivity doesn't exist. Resolution: Please make sure that your workstation has network connectivity. If you are using manual configuration, please double-check the configuration. The network administrator should make sure that the service is running on port 5061 on server OCS_Server_FQDN (IP_address).
This problem occurs either because Communicator 2007 R2 cannot resolve the DNS name of Microsoft Office Communications Server 2007 R2 or because Communicator 2007 R2 cannot make a successful connection to Communications Server 2007 R2.
To resolve this problem, apply the following update:
(http://support.microsoft.com/kb/967673/ )Description of the Communicator 2007 R2 hotfix rollup package: April 2009
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.