On backup or replication of a given VM, the error above is returned and visible in the vRanger Job Detail Log in the following format:
This error is actually thrown by the VMware Virtual Center (attempting a manual snapshot of the VM through the VMWare client will also render the error). It indicates the Datastore storage for the particular VM(s) involved are inaccessible to the VMware Host(s). The most common cause of the issue is bad (dead) SAN-pathing to back-end SAN storage that houses the particular datastore(s).
Check the SAN paths/hardware for defects, correct as needed. Once the storage is operating properly, the error message should disappear.