Attempting to start the observer raises an error: DGMGRL> start observer: DGM-16954: Unable to open and lock the Observer configuration file Failed. Identify two possible reasons for this error. 

Answer options:

A. Fast-Start Failover is not yet enabled for this Data Guard configuration.
B. The observer configuration file is marked read-only.
C. There is already an observer running for this Data Guard configuration.
D. There is another observer running for a Data Guard configuration which uses the same observer configuration file.
E. The broker configuration has not yet been created.

BD

Error code: DGM-16954 - Description: Unable to open and lock the Observer configuration file Cause: The Observer configuration file cannot be opened or cannot be locked for exclusive access. Action: Make sure the Observer has the correct operating system privileges to write the file and there is no other Observer that is using the same file. Try the command again. References: https://www.oraexcel.com/oracle-12cR1-DGM-16954