Cause: The filename supplied as a parameter to the ALTER DATABASE BACKUP
CONTROLFILE command or to cfileSetSnapshotName matches the name of
a file that is currently part of the database.
Action: Retry the operation with a different filename.
Related posts
ORA-00238 Operation would reuse a filename that is part of the database
ORA-00222 Operation would reuse name of a currently mounted control file
Oracle Database Internal Mechanism 