Clustered NSS Volume fails

Hi All,
I hope someone can help me out here.
I have a 5 node OES2 linux cluster running under VMWare ESX 3.5
Periodically NSS volumes are just failing. The /var/log/messages file shows the following errors:

Mar 10 12:33:27 yalnode2 kernel: BIO_UPTODATE not set. Got an IO error
Mar 10 12:33:27 yalnode2 kernel: sd 1:0:4:0: reservation conflict
Mar 10 12:33:27 yalnode2 kernel: sd 1:0:4:0: SCSI error: return code = 0x00000018
Mar 10 12:33:27 yalnode2 kernel: end_request: I/O error, dev sdf, sector 419219536
Mar 10 12:33:27 yalnode2 kernel: BIO_UPTODATE not set. Got an IO error
Mar 10 12:33:27 yalnode2 kernel: sd 1:0:4:0: reservation conflict
Mar 10 12:33:27 yalnode2 kernel: sd 1:0:4:0: SCSI error: return code = 0x00000018
Mar 10 12:33:27 yalnode2 kernel: end_request: I/O error, dev sdf, sector 419219536
Mar 10 12:33:27 yalnode2 kernel: BIO_UPTODATE not set. Got an IO error
Mar 10 12:33:27 yalnode2 kernel: sd 1:0:4:0: reservation conflict
Mar 10 12:33:27 yalnode2 kernel: sd 1:0:4:0: SCSI error: return code = 0x00000018
Mar 10 12:33:27 yalnode2 kernel: end_request: I/O error, dev sdf, sector 419219536
Mar 10 12:33:27 yalnode2 kernel: BIO_UPTODATE not set. Got an IO error
Mar 10 12:33:27 yalnode2 kernel: NSSLOG ==> [Error] comnPool.c[2575]
Mar 10 12:33:27 yalnode2 kernel: Mar 10, 2009 12:33:26 pm NSS<COMN>-4.10b-xxxx:
Mar 10 12:33:27 yalnode2 kernel: Pool SOFTWARE: System data I/O error 20204(zfsSuperBlk.c[2569]).
Mar 10 12:33:27 yalnode2 kernel: Block 52402434(file block 52402434)(ZID 0)
Mar 10 12:33:29 yalnode2 kernel: NSSLOG ==> [Error] zfsVolumeData.c[216]
Mar 10 12:33:29 yalnode2 kernel: Mar 10, 2009 12:33:29 pm NSS<ZLSS>-4.10b-1449:
Mar 10 12:33:29 yalnode2 kernel: Error reading VolumeData Block 36, status=20206.
Mar 10 12:33:29 yalnode2 kernel: NSSLOG ==> [Error] zfsVolumeData.c[216]
Mar 10 12:33:29 yalnode2 kernel: Mar 10, 2009 12:33:29 pm NSS<ZLSS>-4.10b-1449:
Mar 10 12:33:29 yalnode2 kernel: Error reading VolumeData Block 36, status=20206.
Mar 10 12:33:30 yalnode2 kernel: NSSLOG ==> [Error] zfsVolumeData.c[216]
Mar 10 12:33:30 yalnode2 kernel: Mar 10, 2009 12:33:30 pm NSS<ZLSS>-4.10b-1449:
Mar 10 12:33:30 yalnode2 kernel: Error reading VolumeData Block 36, status=20206.
Mar 10 12:33:30 yalnode2 kernel: NSSLOG ==> [Error] zfsVolumeData.c[216]
Mar 10 12:33:30 yalnode2 kernel: Mar 10, 2009 12:33:30 pm NSS<ZLSS>-4.10b-1449:
Mar 10 12:33:30 yalnode2 kernel: Error reading VolumeData Block 36, status=20206.
Mar 10 12:33:31 yalnode2 kernel: NSSLOG ==> [Error] zfsVolumeData.c[216]
Mar 10 12:33:31 yalnode2 kernel: Mar 10, 2009 12:33:31 pm NSS<ZLSS>-4.10b-1449:
Mar 10 12:33:31 yalnode2 kernel: Error reading VolumeData Block 36, status=20206.
Mar 10 12:33:31 yalnode2 kernel: NSSLOG ==> [Error] zfsVolumeData.c[216]
etc..........

Any insights would be much appreciated.