Hello,
What version of SEPM 12.1 are you running?
Secondly, what version of OS are you running?
Is the SEP client remotely installed? How far is this client away from the SEPM machine?
Could you please upload us the System Logs from the SEP client.
The System Logs could be found under:
SEP client >> View Logs >> Virus and Spyware Protection (View Logs) >> System Logs
SEP client >> View Logs >> Client Management (View Logs) >> System Logs
Secondly, please upload us the Sylink.log, which would assist us in understanding the root cause of the issue.
How to enable Sylink debugging for the Symantec Endpoint Protection 11.x and 12.1 client in the Windows Registry
http://www.symantec.com/docs/TECH104758
Hope that helps!!