Oracle Error Message
RMAN-05536: auxiliary logfile name string conflicts with a file used by the target database
Reason for the Error
RMAN attempted to use the specified logfile name as a standby redo log file in the auxiliary database, but this name was already in use by the target database.
Solution
Use or alter LOG_FILE_NAME_CONVERT so that unique logfile names can be generated. Or wait for the command to complete and create standby logfiles using the SQL ALTER DATABASE ADD STANDBY LOGFILE command.