Hi,
Is it happening after upgrade to 12.1 RU5?
After upgrading SEPM to 12.1 RU5, 32-bit virus definitions do not update
Fix ID: 3671931
Symptom: After a Symantec Endpoint Protection Manager upgrade to 12.1 RU5, the 32-bit Virus and Spyware definitions are not up to date.
Solution: Gave the semsrv and semwebsrv accounts full access to the LiveUpdate symcData folder.
OR
Download .jdb files to update definitions for Endpoint Protection Manager
http://www.symantec.com/docs/TECH102607
After SEPM manual update, next liveupdate schedule should update all the defintions without any issue.