Oracle Message ORA-10456 - cannot open standby database; media recovery session may be in progress

ERRORcannot open standby database; media recovery session may be in progress
CAUSEA media recovery, RMAN, or flashback database session may have been in progress on a mounted instance of a standby database when an attempt was made to open the standby database.
ACTIONCheck for and cancel any conflicting recovery session and open the standby database.