When creating a file based backup with vcbmounter.exe or pre-command.wsf the backup fails with the following error:

[YYYY-MM-DD HH:MM:SS.SSS 'vcbMounter' 5716 error] Error: Error while opening disk blklst://snapshot-441[Production] SERVER/SERVER.vmdk@domain.com?xxxx/xxxx: A virtual disk could not be opened. -- Cannot open disk file: Error : Disk library failed (One LUN could not be opened). Unable to open 'blklst://snapshot-441[Production] SERVER/SERVER.vmdk@domain.com'. Failed to configure disk scsi0:0.

[YYYY-MM-DD HH:MM:SS.SSS 'vcbMounter' 5716 error] An error occured, cleaning up...

The datastore has two LUNs with the extent being used through a separate controller/target ID.

Both LUNs need to be presented on the same Controller/Target ID:

- Move both LUNs to the same Controller/Target ID
- In Computer Management right click on Storage | Disk Management and select Rescan Disks
- Restart the VMware Virtual Mount Manager Extended service on the VCB Proxy