Below is an excerpt from the Symantec Antivirus knowledgebase, Symantec antivirus, although it updates the same as before, doesn't recognize a date newer than 2009.The fix: release new definition updates, but keep the December 31, 2009 date.
This document will be updated as soon as more information becomes available.
I tried to manually launch Live Update on SEPM various times, but no use, Every time update all other definitions excluding Antivirus updates.
After few minutes , it will automatically push the definition to SEPM console and it will be distributed to clients in few minutes, All of my clients (100 ) took about 20 minutes to update.
If you need help with Symantec products, you can post in the Symantec forums.
FYI These forums are for the home user oriented Norton product line.