When you add the Active Directory Schema Manager snap-in to the MMC, it may not connect to the Operations Master. If you try to view the permissions on the schema, you may receive:

Could not connect to the current schema master server. The server may not be available, or you may have insufficient privileges to manage the schema.

If you try to change or view the Operations Master, you receive:

The server is currently offline.

To fix the problem, expand the hive by pressing the +. Now you can connect the snap-in the the Operations Master.