If the client and the server do not communicate, you may need to replace the Sylink.xml file on the client computer to restore communications. You can manually export the Sylink.xml file from Symantec Endpoint Protection Manager on a group basis.
The most common reasons for replacing the Sylink.xml on the client are:
To convert an unmanaged client into a managed client.
To reconnect a previously orphaned client to the management server.