Quote from http://blogs.technet.com
A potential problem with Volume Manager on Windows Server 2008 systems may lead to data loss.
This hot fix is not DPM-specific. However, because DPM servers do utilize dynamic disks, it is important to apply this hotfix on WS08-based DPM servers so that your backup-data is not lost from the DPM storage pool.
For more information please read the link below to the hot fix.
962975 Dynamic disks are marked as "Invalid" on a computer that is running Windows Server 2008 or Windows Vista when you bring the disks online, take the disks offline, or restart the computer if Data Protection Manager is installed
This hot fix does not apply to Windows Server 2008 R2