Oracle Message ORA-16649 - possible failover to another database prevents this database being opened

ERRORpossible failover to another database prevents this database being opened
CAUSEAn attempt to open the database was made either when a failover occurred or while fast-start failover was enabled and the fast-start failover status could not be evaluated.
ACTIONCheck if a failover did occur. If fast-start failover is enabled, and a failover did not occur, ensure that connectivity exists between this database and either the observer or the target standby database. Then, try opening the database again.