Hello,
What version of SEP 12.1 are you carrying? Is that SEP 12.1.1000 (RU1)?
If not, I would recommend you to Migrate to the Latest version of SEP 12.1 RU1 as there are couple of fixes done in the Latest version. Check this Article:
New fixes and features in Symantec Endpoint Protection 12.1 Release Update 1
http://www.symantec.com/docs/TECH174565
Again, you could also check this Article: SONAR Definitions are not updated on SEP 12.1 Clients.
http://www.symantec.com/docs/TECH178125
Secondly, Are the clients updated? What is the date format selected?
Check this Article:
http://www.symantec.com/business/support/index?page=content&id=TECH164272
Hope that helps!!