This what I found and might help.
symptom: Launching Oracle Expert fails
symptom: org.omg.CORBA.NO_IMPLEMEMT(completed=MAYBE)

cause: The Expert tool uses the tnsnames.ora file in the Oracle Enterprise Manager (EM) home to connect to the Oracle Management Server (OMS) repository. The service name that the tool looks for is the service name specified in the EM Configuration Assistant. The service name used in the Oracle Enterprise Manager Configuration Assistant does not match an entry in the tnsnames.ora file in the EM home.


http://metalink.oracle.com/metalink/..._id=220944.996

http://metalink.oracle.com/metalink/...p_id=22662.996