The error DGM-16954 indicates that the observer configuration file cannot be opened or locked for exclusive access. This could happen if the observer configuration file is marked as read-only, preventing it from being opened for writing. Additionally, if another observer is already using the same configuration file, it would cause a failure to lock the file, leading to the same error. Therefore, the two possible reasons for this error are that the observer configuration file is marked read-only and that there is another observer running for a Data Guard configuration which uses the same observer configuration file.