This monitor verifies that the PDC and the local DC agree on which server holds the Schema Master FSMO role.
Possible causes include the following:
There is an AD replication problem in the domain.
Ensure that the domain controller is online and functioning correctly.
Ensure that DNS is properly resolving the domain controller's IP address.
Check that dcdiag is not returning any problems.
Check that repadmin is not showing any problems with AD replication.