Problem while adding a computer using SBS 2011 Essentials connector

Hi experts,
I have been facing a problem while adding a computer using SBS 2011 Essentials connector.
It says an unknown error has occurred.
You need to know that the customer has migrated from Windows 2003 to Windows SBS 2011 Essentials.
Please look at the screenshot.

Cannot connect this computer to the network
An unexpected error has occurred. For more information, see troubleshoot connection computer to the server.
Close
Please provide necessary suggestion in respect of the issue.
Thanks in Advance.
