Check if the GUP is recognized as a GUP by checking if the SharedUpdates folder is in the client's SEP root folder (e.g., C:\Program Files (x86)\Symantec\ Symantec Endpoint Protection\SharedUpdates). If it is a 32-bit operating system then it will be located in the Program Files\Symantec\Symantec Endpoint Protection\SharedUpdates folder instead.
Is the designated GUP configured as a GUP and listening on port 2967 (default port)? Use netstat to check the connection state table.
Are the SEP clients that are requesting content from a GUP configured to use a GUP as their Liveupdate source? Check the following: