A potential problem with Volume Manager on Windows Server 2008 and Windows Vista systems may lead to data loss. This hot fix does not apply to Windows Server 2008 R2.
Microsoft recommends that you apply this hotfix on any Windows Server 2008 and Windows Vista platforms that are currently in use or are using dynamic disks.
This hot fix is not DPM-specific. However, due to DPM's utilization of dynamic disks, it is critical to apply this hotfix on WS08-based DPM servers so that your backup-data is not lost from the DPM storage pool. It is critically important to have this hotfix applied to your Vista clients as well if they are using dynamic disks.
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