Did you recently promote a DC and are seeing the following events? I did, and it got me searching around. Apparently this is normal and safe to ignore. Via the Microsoft KB 268329...
Internal event: The following schema class has a superclass that is not valid.
Class identifier: 752255955
Class name: msExchEdgeSyncMservConnector
Superclass identifier: 752255954
Inheritance was ignored.
Wondering what a superclass is?