RMAN-03009: failure of allocate command on sbt_1 channel

Hi,

I am looking to take RMAN online backup using BR* Tools.

I have configured the parameter in initSID.sap for RMAN backup onto disk.

o backup_dev_type = rman_disk

o tape_copy_cmd = rman

o disk_copy_cmd = rman

But when i start the backup it is failing with the below error message (although the backup device type is disk)

RMAN-0300: failure of allocate command on str1 channel

ORA-19554: error allocating device, device_type=SBT_TAPE and device_name:

ORA-27211:Failed to load Media Management Library.

Can some help me in sorting the same.

Regards

Mahendra K