Oracle Error Message
ORA-01232: cannot start online backup – file string is being made read-only
Reason for the Error
An attempt to start an online backup found that one of the files is in transition to read-only mode.
Solution
Wait for the transition to complete and then retry the command, if this is an ALTER DATABASE BEGIN BACKUP command, or take the backup without any begin or end commands, if this is an ALTER TABLESPACE BEGIN BACKUP command.