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DGM-16979:

Unable to log on to the primary or standby database as SYSDBA
Cause: The username/password used by the observer to log on to the primary database and fast-start failover target standby database does not have valid SYSDBA credentials.
Action: Make sure the primary database and Fast-start failover target database are using a remote login password file. Make sure the SYSDBA password is the same at both databases and that the SYSDBA password is used in the CONNECT command. Start the observer again.