Two days ago on our SCOM 2012 Sp1 we got the alert
All Management Servers Resource Pool Unavailable:
Since then no alerts are being generated by operations manager except this one.
I also see error 2000 in the Operations Manager event log for all our managed server:
A device which is not part of this management group has attempted to access this Health Service.
I also notice that the systems center server itself is not being monitored.
We have only one operations manager server and the database is on that server.