Windows XP and Windows 7 clients not getting update from SEPM

Most SEP clients update the definitions as expected but a few hundred clients (windows XP and windows 7)won't update at all.

SEPM and client version:12.1 RU6 MP5

Trouble Shooting so far:

1. Clearing corrupt defs as described in this artical:     

   http://www.symantec.com/business/support/index?page=content&id=TECH103176&locale=en_US#

2. Restart the SMC (smc -stop...)
3. Uninstall and reinstall SEP client manually
4. Unistall SEP client then push out SEP client from SEPM 

After performed above steps,issue has been resolved but practically it is not possible to perfom this steps on each client system.

Please help,around 102 sep clients (windows XP and windows 7) are out of date showing error visrus definitions are coruupted or missing.