Snapshot provider error (0x138E) The cluster resource is not available when backing up a Hyper-V guests on a Hyper-V Cluster Shared Volume (CSV)
When backing up a Hyper-V HA cluster virtual machines that reside on a Clustered Shared Volumes (CSV) the job fails with the following error (FIGURE 1):
Completed status: Failed
Final error: 0x138e - The cluster resource is not available.
Final error category: Other Errors
For additional information regarding this error refer to link V-79-0-5006
AOFO: Initialization failure on: "VRTSRV::\\HOST\Hyper-V?HA?VM\GUEST\". Advanced Open File Option used: Microsoft Volume Shadow Copy
Snapshot provider error (0x138E): The cluster resource is not available.
Check the Windows Event Viewer for details.
Debugging the Backup Exec Remote agent service on the Active Hyper-V cluster node the following error is present in the debug log:
BEREMOTE DEBUG LOG:
 04/02/10 11:01:06 VssSnashotVolume::PrepareClusterSharedVolumesForSnapshot_() - ERROR: ClusterPrepareSharedVolumeForBackup failed for C:\CLUSTERSTORAGE\
 04/02/10 11:01:06 Error (0x138e) from VSS - Unknown error code
 04/02/10 11:01:06 after calling function: VssSnashotVolume::PrepareCSVVolumesForSnapshot_
 04/02/10 11:01:06 VssSnashotVolume::PrepareToSnapVolumeSet() - done. LastError_: 138e
 04/02/10 11:01:06 Error SnapshotBackupEngine::snap_file_systems failed.
 04/02/10 11:01:06 ndmpdSnapshotPrepare2: Snapshot error. ErrorCode: 0x138e ErrorLevel: 2 Error Src: 2
 04/02/10 11:01:06 ndmpdSnapshotPrepare2: sending reply...
 04/02/10 11:01:06 VSS AbortBackup called successfully
The issue occurs when CSV volume mount point has been created\renamed, and either has _ (underscore)/special characters OR the folder name has characters equal to 15 or more.
Other combinations using Hypen's, special characters, and underscores with a CSV mount point folder greater than 8 characters may experience the same issue.
In the above debug log the CSV was renamed from the default Windows C:\ClusterStorage\Volume1 to C:\Clusterstorage\VIRTUALMACHINES where "VIRTUALMACHINES" is 15 characters in length.
A hotfix (TECH146017) is now available for this issue in Backup Exec 2010 R2. Refer to the Hotfix link under Related Documents at the end of this article to obtain the hotfix needed to resolve the issue.