If you try to take the backup of a controlfile and it returns ORA-00236, it means that you are trying to take backup of a controlfile that is already a backup. The scenario is that you are performing recovery of a database, and during this process, you restored the backup of controlfile. Before recovery is completed and database is opened, the status of controlfile remains “backup”, and trying to backup the controlfile would return ORA-00236.
Following is a real time scenario when I faced this problem.
