corrupted virus definitions present on the SEPM prevent the SEPM's ability to update the SEP clients with new virus definitions

I upgraded SEPM version 11.0.7101.1056 to version 12.1.2015.2015 two month ago. since I had four or five times problem that discribed at this Article:
http://www.symantec.com/business/support/index?page=content&id=TECH166923

Why this happening may be anybody know?