Firstly, I would suggest upgrading to the latest version of SEP, RU6 MP2 (11.0.6200.754)
If that does not fix it or you can't upgrade at this time, try disabling tamper protection:
To do this on the client:
Change Settings >> To the right of Client Management click the Configure Settings button >> Tamper Protection tab >> uncheck the box for "Protect Symantec security software from being tampered with or shutdown"
I wouldn't suggest disabling tamper protection permanently, but I had a similar issues with Notes 8.5.1 FP1 and this worked. Ultimately, we upgraded to Notes 8.5.1. FP3 and it went away even with tamper protection enabled.