VMWare snapshot is failing: Status 156 - The operation is not allowed in the current state.

Problem

Virtual machine backup is failing during snapshot creation.

Error Message

9/16/2014 10:04:45 AM - Info bpfis(pid=4552) Backup started
9/16/2014 10:04:45 AM - snapshot backup of client clddrt01 using method VMware_v2
9/16/2014 10:07:05 AM - Critical bpbrm(pid=8876) from client <vm_name>: FTL - VMware snapshot failed: SYM_VMC_TASK_REACHED_ERROR_STATE
9/16/2014 10:07:05 AM - Critical bpbrm(pid=8876) from client <vm_name>: FTL - VMware error received: The operation is not allowed in the current state.
9/16/2014 10:07:05 AM - Critical bpbrm(pid=8876) from client <vm_name>: FTL - snapshot processing failed, status 156
9/16/2014 10:07:06 AM - Critical bpbrm(pid=8876) from client <vm_name>: FTL - snapshot creation failed, status 156
9/16/2014 10:07:06 AM - Warning bpbrm(pid=8876) from client <vm_name>: WRN - ALL_LOCAL_DRIVES is not frozen
9/16/2014 10:07:06 AM - Info bpfis(pid=4552) done. status: 156
9/16/2014 10:07:06 AM - end VMware, Create Snapshot; elapsed time: 00:02:29
9/16/2014 10:07:06 AM - Info bpfis(pid=0) done. status: 156: snapshot error encountered
9/16/2014 10:07:06 AM - end writing
Status 156
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9/16/2014 10:07:12 AM - end Parent Job; elapsed time: 00:02:37
snapshot error encountered(156)
 

Cause

In vSphere client, virtual machine shows as greyed out and "inaccessible." 

In this case the virtual machine's datastore had been removed but the virtual machine itself was still in the vCenter inventory resulting in an inaccessible virtual machine.

During snapshot creation attempt the following message was display in vCenter events 

"The operation is not allowed in the current state."
 

Solution

Take corrective action within vCenter to fix this virtual machine.  This might be to remove the virtual machine from the vCenter inventory, or correct the datastore.  If no corrective action is taken  the virtual machine should be removed from the backup policy.