Recently we started receiving alerts our restores were failing due to the VSS provider is in a bad state.   When attempting to manually recovery a SQL DB we saw the same error in the DPM console.  Everything checked out fine, VSS was healthy, other restores were working fine, except this 500gb DB restore.  The root cause was disk space AVAILABLE, for this large DB.  There were no alerts for low disk space from SCOM, but the DB required more than available disk space, and the error generated through DPM was an unhealthy VSS provider.