snapshot error

 hi,
VVR 5.1
snop shot gives an error
license is ok,enabled.
we reboot the machine but same issue is exists.

ID:
V-106-58644-5097
Received:
Thursday, May 28, 2009 1:56:55 PM EEST
Severity:
Error
Source:
StorageAgent@srvistfil50.tr.world.socgen
Classification:
VVR Class
Brief Description:
SHARERDS: Snapshot failed on RVG SHARERVG.
Details:
Failed to take a snapshot of data volumes in the RVG.
Recommended Action:
Make sure that each data volume has at least one snapstarted plex
associated with it and the snapshot mirror is synchronized. If these
requirements are already satisfied, the command might have failed due to
an overlap between the RVG disks and the disk(s) used by one or more
snapshot ready plexes.
Other Properties:
None


i think ,problem may cause disc or vss .
what is you idea?
i also attached related error screen.
thanks...