Failed to Validate Disk Arbitration

When I validate my cluster configuration, I got the follwing results:

List All Disks Success
List Potential Cluster Disks Success
Validate Disk Arbitration Failed
Validate SCSI-3 Persistent Reservation Success

My configuration:
1) Two nodes' windows 2008 cluster with a shared FC array.
2) No MPIO is installed.

Cluster log file of one node reports the error "OnlineThread: Unable to
arbitrate for the disk. Error: 1235" and another node's log file reports the
error "ERR [RES] Physical Disk <Cluster Disk 2>: Open: Unable to get disk
identifier. Error: 5023.".

After I create a cluster, I try to bring the FC disk to online and but it
can't be brought online. The failed reason is still the error "OnlineThread:
Unable to arbitrate for the disk. Error: 1235". After my array handled
"register","reserve"of PRO, "read key" of PRI, I don't know why "unregister"
of PRO is received by array.
What is the process of "Disk Arbitration" of Win2k8 cluster service? What
is the cause of above error "OnlineThread: Unable to arbitrate for the disk.
Error: 1235"?

Can any one give some clues for me?
thanks very much.



__________ Information from ESET NOD32 Antivirus, version of virus signature database 4090 (20090520) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com