Cannot load tape during scheduled backup

Dear all,
I have this problem during my scheduled backup.When a backup is scheduled to start, it failed to load the tape in the pool and after a while, the whole server hung. The tape is already labelled and is in the magazine. However, the existing tape in the drive could not eject automatically and load up the requested tape.

Below is the error logs I have captured.

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09/05/06 15:20:00 nsrd: savegroup info: starting POR03 (with 1 client(s))
09/05/06 15:20:00 nsrd: savegroup info: orix:/tmp: No full backups of this save set were found in the media database; performing a full backup
09/05/06 15:20:00 nsrd: Operation 22 started : Load volume `POR.03'.
09/05/06 15:20:00 nsrd: media waiting event: Waiting for 1 writable volumes to backup pool 'Por3' tape(s) on backup
09/05/06 15:20:02 nsrmmd #2: Start nsrmmd #2, with PID 28377, at HOST backup
09/05/06 15:20:04 nsrd: [Jukebox `Legato', operation # 22]. Cannot find an available nsrmmd service for operation on device '/dev/nst0'. Try again.
09/05/06 15:20:04 nsrmmgd: Cannot find an available nsrmmd service for operation on device '/dev/nst0'. Try again.
09/05/06 15:20:04 nsrmmgd: Jukebox `Legato' failed to load the requested volume.
09/05/06 15:20:08 nsrd: [Jukebox `Legato', operation # 22]. Finished with status: retryable
09/05/06 15:20:08 nsrmmgd: RAP error: Invalid resource data.
09/05/06 15:20:08 nsrmmgd: Cannot update operation status resource (instance 22).
09/05/06 15:20:10 nsrd: media info: Suggest manually labeling a new writable volume for pool 'Por3'
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