Check Connectivity between Symantec Antivirus Client & Symantec Endpoint Management Server.:

Check Connectivity between SEP & SEPM:

1. Do a Secars test to Test Connectivity between SEP and SEPM
Testing Communication from an Endpoint Protection client to the Endpoint Protection Manager
[ http://service1.symantec.com/support/ent-security.nsf/854fa02b4f5013678825731a007d06af/a6b9dc2d869c89a58825737700642895?OpenDocument ]
2. Get the sylinkmonitor logs to check the communication for any errors
SylinkWatcher and SylinkMonitor - tools for real-time debugging of SPA 5.x and SEP 11.x
http://service1.symantec.com/support/ent-security.nsf/854fa02b4f5013678825731a007d06af/4be077e14183395388257348007a2472?OpenDocument

Remove corrupt definitions
1. How to clear out corrupted definitions for a Symantec Endpoint Protection Client [ http://service1.symantec.com/support/ent-security.nsf/854fa02b4f5013678825731a007d06af/691fb01f62f2a700882573c2006d6de7?OpenDocument ]

Check if SEPM has Latest Definitions:
1. Open SEPM->Admin->Servers->Local Site
2. Show Liveupdate Downloads
3. Make sure that the date for 32 bit and 64 Definitions for ‘Virus & Spyware Definitions’ is up-to-date.