Netback ndmp backup failing

[Steven_Porter]

I have netbackup 5.0 mp5
A neo 2000 tape robot with 1 tape drive connected to the W2K server running Netbackup, and 1 tape drive connected to a Net App filer.
Backups across the LAN from various servers to the robot work OK
The NDMP backup from the Net App filer fails very regularly, the backup job starts and then the drive downs and thats it.

C:\Program Files\VERITAS\Volmgr\bin>set_ndmp_attr -probe nafox
Host "nafoxford" tape device model "Quantum DLT8000":
Device "rst0l" attributes=(0x5) REWIND RAW
DENSITY=85937 bpi 35 GB
ELECTRICAL_NAME=1a.2
SERIAL_NUMBER=PMC05P0143
WORLD_WIDE_NAME=
ALIAS 0=st0
Device "nrst0l" attributes=(0x4) RAW
DENSITY=85937 bpi 35 GB
ELECTRICAL_NAME=1a.2
SERIAL_NUMBER=PMC05P0143
WORLD_WIDE_NAME=
ALIAS 0=st0
Device "urst0l" attributes=(0x6) UNLOAD RAW
DENSITY=85937 bpi 35 GB
ELECTRICAL_NAME=1a.2
SERIAL_NUMBER=PMC05P0143
WORLD_WIDE_NAME=
ALIAS 0=st0
Device "rst0m" attributes=(0x5) REWIND RAW
DENSITY=85937 bpi 70 GB (w/comp)
ELECTRICAL_NAME=1a.2
SERIAL_NUMBER=PMC05P0143
WORLD_WIDE_NAME=
ALIAS 0=st0
Device "nrst0m" attributes=(0x4) RAW
DENSITY=85937 bpi 70 GB (w/comp)
ELECTRICAL_NAME=1a.2
SERIAL_NUMBER=PMC05P0143
WORLD_WIDE_NAME=
ALIAS 0=st0
Device "urst0m" attributes=(0x6) UNLOAD RAW
DENSITY=85937 bpi 70 GB (w/comp)
ELECTRICAL_NAME=1a.2
SERIAL_NUMBER=PMC05P0143
WORLD_WIDE_NAME=
ALIAS 0=st0
Device "rst0h" attributes=(0x5) REWIND RAW
DENSITY=98250 bpi 40 GB
ELECTRICAL_NAME=1a.2
SERIAL_NUMBER=PMC05P0143
WORLD_WIDE_NAME=
ALIAS 0=st0
Device "nrst0h" attributes=(0x4) RAW
DENSITY=98250 bpi 40 GB
ELECTRICAL_NAME=1a.2
SERIAL_NUMBER=PMC05P0143
WORLD_WIDE_NAME=
ALIAS 0=st0
Device "urst0h" attributes=(0x6) UNLOAD RAW
DENSITY=98250 bpi 40 GB
ELECTRICAL_NAME=1a.2
SERIAL_NUMBER=PMC05P0143
WORLD_WIDE_NAME=
ALIAS 0=st0
Device "rst0a" attributes=(0x5) REWIND RAW
DENSITY=98250 bpi 80 GB (w/comp)
ELECTRICAL_NAME=1a.2
SERIAL_NUMBER=PMC05P0143
WORLD_WIDE_NAME=
ALIAS 0=st0
Device "nrst0a" attributes=(0x4) RAW
DENSITY=98250 bpi 80 GB (w/comp)
ELECTRICAL_NAME=1a.2
SERIAL_NUMBER=PMC05P0143
WORLD_WIDE_NAME=
ALIAS 0=st0
Device "urst0a" attributes=(0x6) UNLOAD RAW
DENSITY=98250 bpi 80 GB (w/comp)
ELECTRICAL_NAME=1a.2
SERIAL_NUMBER=PMC05P0143
WORLD_WIDE_NAME=
ALIAS 0=st0

The Device used is the nrst0a

C:\Program Files\VERITAS\Volmgr\bin>tpconfig -d
Index DriveName DeviceName Type Shared Status
***** ********* ********** **** ****** ******
0 QUANTUM80000 \\.\Tape0 dlt No UP
TLD(0) Definition DRIVE=1
1 QUANTUMDLT80001 /ndmp/nrst0a dlt No DOWN
TLD(0) Definition DRIVE=2

Currently defined robotics are:
TLD(0) SCSI port = 2, bus = 0, target = 6, lun = 0,
volume database host = oxf_backup

I can verify the ndmp authentication is OK
C:\Program Files\VERITAS\Volmgr\bin>set_ndmp_attr -verify
Verify Host name: nafoxford
Connecting to host "nafoxford" as user "root"...
Waiting for connect notification message...
Opening session--attempting with NDMP protocol version 4...
Opening session--successful with NDMP protocol version 4
host supports TEXT authentication
Logging in using TEXT method...
Host info is:
host name "nafoxford"
os type "NetApp"
os version "NetApp Release 6.4.5"
host id "0033606129"
Login was successful
Host supports LOCAL backup/restore
Host supports 3-way backup/restore

The entry in bptm that always occurs when the backup fails is

14:47:56.096 <2> bptm: INITIATING (VERBOSE = 0): -count -cmd -rt 8 -rn 0 -stunit NDMP_NetAPP -den 13 -mt 3 -masterversion 500000 -c nafoxford.uk.linde-k
14:47:56.111 <4> bptm: all drives are down for the specified robot number = 0, robot type = TLD and density = dlt
14:47:56.111 <2> bptm: EXITING with status 0 <----------

I have tried physically swapping the 2 tape drives, deleting each device in netbackup, synchronising the global db, and then re-adding the devices

one problem I have identified is that I cannot browse for the tape drive that is connected to the Net App filer, I can only add this in manually, and there for a serial number is not shown from the admin consol device list (last column)
any ideas?