Stored shadow copies are overwritten in Microsoft System Center Data Protection Manager 2006
Stored shadow copies of backup replicas are overwritten even if there is sufficient storage space allocated for shadow copies in Microsoft System Center Data Protection Manager (DPM) 2006. This symptom typically only affects protected volumes with less than 25 gigabytes (GB) of data.
This problem occurs because DPM 2006 incorrectly determines the minimum required disk space threshold that is used to allocate space for shadow copy storage on the DPM 2006 server. The Volume Shadow Copy Service (VSS) uses a minimum disk space threshold for shadow copy area disk allocations. When the threshold for the minimum disk space that is required is incorrect, stored shadow copies can be overwritten.
A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that this article describes. Apply it only to systems that are experiencing this specific problem.
To resolve this problem, contact Microsoft Product Support Services to obtain the hotfix.
More Information: Microsoft KB Article 910330