Upgrade all the affected clients to 12.1 RU2 to resolve the issue.
Please see the following KB article for migration to SEP 12.1 RU2.
http://www.symantec.com/business/support/index?page=content&id=TECH197426
Applies To
SEPM - 12.1 RU2
Clients - 12.1 RU1 MP1
Operating system - Windows 7 Professional Edition
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