Do you have millions of SecurityCenter Errors in your SEM for many hosts? ProviderSID SecurityCenter 17? SourceAccount Unable to resolve username.
If you do I found out what's causing them... it's 3rd party security products like SEP. I use SEP and have these many many events in SEM... too many. Event ID 17 is Security Center failed to validate caller with error %1. This is an error generate due to issues with Microsoft AM PPL feature... whatever that is???
Good news! I found out the Symantec Endpoint Protection 14.2 RU1 or newer fixes this error in SEM. MS says it's a 3rd party security software problem. I'm moving my hosts to newer SEP and finally this noise of errors is going away!