Vista Tutorial - Virtual Server 2005 R2 msvmscsi error

Hello,

We are experiencing a problem with Virtual Sever 2005. Here is our
setup:

Physical Server: Dual 3.0GHz XEONs, 10GB RAM, Dell PERC 4e/Si RAID
adapter (2 SCSI drives on RAID 1)

HOST OS: Windows Server 2008 Standard Edition (32bit). Has the
Aplication Server role installed, along with Virtual Server 2005 R2
(1.1.629.0 EE R2 SP1.) This server's only funtion is to host the
Virtual environment.

Virtual Machine 1: Windows Web Server 2008. Serving a two low-
traffic .NET 2.0 sites.
Virtual Machine 2: Windows Server 2008 Standard Edition. SQL Server
2008 Standard Edition.

The problem:

On Virtual Machine 2 we have a SQL maintenance plan to backup all user
databases (3 databases, approximately 2.0GB combined) in the middle of
the night, when the server utilization basically zero. About 15-30
seconds into the backup, the event log starts logging msvmscsi errors
(event 9, the device did not respond within the timeout period.) The
backup completes in about 2 minutes, but the msvmscsi errors persist
for about 15 minutes. Eventually, the entire OS stops responding
(pings are returned, but can't RDP in or connect to SQL.) Then, after
another 5-10 minutes, the msvmscsi errors stop, and the system is
responsive again (usually, however sometimes we have to reset the
guest OS to get it back.)

I have updated Virtual Server with the most recent update I can find
(which specifically says it added Sever 2008 support) and updated the
virtual machine add-ins on the guest OSes, to no avail. I have also
modified the registry to increase the timeout on the msvmsci device
and that also has had no effect. I have also had the backup job
attempt to write the backup files to both a Local VHD and to a VHD on
our SAN, with the same results.

It is worth noting, that the failure is only on the second virtual
machine, the Host and the first virtual machine are happy and
responsive while the second one is floundering.

Any ideas?