SBS 2008 Backup failing With Error Code '2155348256'

My sbs backup has been failing the last few days with the above error code.

below is a copy of the event logs, any ideas?

EventData

  BackupTemplateID {7AF9B42D-FFAD-40E0-AF79-9A285E6DAEEC}
  HRESULT 2155348256
  BackupState 12
  BackupTarget Backup Drive 1
  NumOfVolumes 2
  BackupTime 2012-03-26T05:00:01.613Z
  HRESULT 2155348256
  VolumesInfo <VolumeInfo><VolumeInfoItem Name="C:" OriginalAccessPath="C:" State="7" HResult="-2139619299" DetailedHResult="0" PreviousState="15" DataTransferred="0" NumUnreadableBytes="0" TotalSize="0" Flags="0" SSBTotalNoOfFiles="0" SSBTotalSizeOnDisk="0" SSBVhdSize="0"/><VolumeInfoItem Name="E:" OriginalAccessPath="E:" State="15" HResult="-2139619228" DetailedHResult="0" PreviousState="0" DataTransferred="0" NumUnreadableBytes="0" TotalSize="0" Flags="0" SSBTotalNoOfFiles="0" SSBTotalSizeOnDisk="0" SSBVhdSize="0"/></VolumeInfo>
  DetailedHRESULT 2147942402
  SourceSnapStartTime 2012-03-26T05:00:01.606Z
  SourceSnapEndTime 2012-03-26T05:00:54.108Z
  PrepareBackupStartTime <TimesList><Time Time="1601-01-01T00:00:00.000Z" /><Time Time="1601-01-01T00:00:00.000Z" /></TimesList>
  PrepareBackupEndTime <TimesList><Time Time="1601-01-01T00:00:00.000Z" /><Time Time="1601-01-01T00:00:00.000Z" /></TimesList>
  BackupWriteStartTime <TimesList><Time Time="1601-01-01T00:00:00.000Z" /><Time Time="1601-01-01T00:00:00.000Z" /></TimesList>
  BackupWriteEndTime <TimesList><Time Time="1601-01-01T00:00:00.000Z" /><Time Time="1601-01-01T00:00:00.000Z" /></TimesList>
  TargetSnapStartTime 1601-01-01T00:00:00.000Z
  TargetSnapEndTime 1601-01-01T00:00:00.000Z
  DVDFormatStartTime <TimesList></TimesList>
  DVDFormatEndTime <TimesList></TimesList>
  MediaVerifyStartTime <TimesList></TimesList>
  MediaVerifyEndTime <TimesList></TimesList>
  BackupPreviousState 7
  ComponentStatus <ComponentStatus><ComponentStatusItem Name="b9dff3ae-42ea-4db1-a667-4d9d66fd873f" LogicalPath="Microsoft Exchange Server\Microsoft Information Store\THOMASDAVID-SBS" AppId="Exchange" WriterId="{76fe1ac4-15f7-4bcd-987e-8e1acb462fb7}" ConsistencyCheckResult="0" ConsistencyCheckResultDetailed="0"/><ComponentStatusItem Name="2734b1c7-fbfd-4f9e-b0ff-d4c1abb67744" LogicalPath="Microsoft Exchange Server\Microsoft Information Store\THOMASDAVID-SBS" AppId="Exchange" WriterId="{76fe1ac4-15f7-4bcd-987e-8e1acb462fb7}" ConsistencyCheckResult="0" ConsistencyCheckResultDetailed="0"/></ComponentStatus>
  SSBEnumerateStartTime 1601-01-01T00:00:00.000Z
  SSBEnumerateEndTime 1601-01-01T00:00:00.000Z
  SSBVhdCreationStartTime 1601-01-01T00:00:00.000Z
  SSBVhdCreationEndTime 1601-01-01T00:00:00.000Z
  SSBBackupStartTime 1601-01-01T00:00:00.000Z
  SSBBackupEndTime 1601-01-01T00:00:00.000Z
  SystemStateBackup false