You tried to save the log area, either by starting an interactive log backup or by attempting to activate the automatic log backup. This is not allowed in the current database state, because redo log management is disabled. Disabling redo log management canceled the backup history, and the last data backup can no longer be used to fully restore the database instance. Therefore, it doesn't make any sense at present to back up the log.
1. Re-enable redo log management.
2. Create a complete data backup to begin the backup history again.
3. Repeat the failed command.