Hi,
SEP repair should take care if any DLL is missing or corrupt.
Also there was a known issue & fixed in SEP 12.1 RU3 version.
Fix id info:
Windows Action Center incorrectly reports that Symantec Endpoint Protection virus protection is off
Fix ID: 2646137
Symptom: Windows Action Center incorrectly reports Symantec Endpoint Protection virus protection is off. Microsoft Network Access Protection may quarantine client computers as a result.
Solution: When Windows Action Center cannot retrieve Auto-Protect's status, it reports that virus protection is off. A forced update from Symantec Endpoint Protection to Windows Action Center now occurs when the Auto-Protect status goes from Disabled to Enabled, or from 'not able to get status' to Enabled.
Reference: New fixes and features in Symantec Endpoint Protection 12.1.3
http://www.symantec.com/docs/TECH206828