Oracle Message RMAN-06748 - no or more than one tertiary storage channel found

ERRORno or more than one tertiary storage channel found
CAUSERECOVERY FILES, RECOVERY AREA or DB_RECOVERY_FILE_DEST option was specified in BACKUP command, but no or more than one tertiary channel was found. One of the following could have caused this error: 1) All of the allocated channels are of type DISK. 2) No tertiary storage (SBT) channel configured. 3) CHANNEL or DEVICE TYPE option specified is of DISK type. 4) More than one tertiary storage channel allocated or configured and no DEVICE TYPE or CHANNEL option specified.
ACTIONOne of the following: 1) Allocate a channel of TYPE SBT. 2) Configure a SBT channel. 3) Specify CHANNEL, DEVICE TYPE option of TYPE SBT.