Disk shadow on Windows 2008

I have try to backup my virtual machines on my Windows 2008.
I have try some scripts found on the Net with "writer verify ...", but no success.
I have simply remove this line and verify if the backup will be OK.

The contents of the DSH script is (Hyper-V_Backup.dsh) :

set context persistent
set metadata c:\metadata.cab
set verbose on

add volume d: alias VirtualMachinesVolume

begin backup

create
expose %VirtualMachinesVolume% p:
exec C:\Scripts\Hyper-V_Backup\CopyVirtualMachines.cmd
delete shadows exposed p:

end backup

The "CopyVirtualMachines.cmd" is a simple script that use the ROBOCOPY tool to copy the files on the SAN iSCSI.

Useful information :

• http://blogs.technet.com/josebda/archive/2008/05/29/installing-the-vss-hardware-provider-for-the-microsoft-iscsi-software-target-on-windows-server-2008.aspx
• http://tipsfortechies.spaces.live.com/blog/cns!2A1FE102A680A44!198.entry?wa=wsignin1.0&sa=777358495