VMware_thaw: Unable to unlock virtual machine

Has anyone run accross this error, VMware_thaw: Unable to unlock virtual machine? The snapshot job will complete with a status 1, while the backup job will completed with a status 0. This is happening while backing up VM's in our environment. The Master server is a physical server running RedHat 6, and the media server is a VM, running RedHat 6 as well. We are running on NBU version 7.6.0.1. This happened while backing up a VM using the HOTADD method. Below are the job details...

 

03/19/2014 19:50:59 - Info nbjm (pid=4387) starting backup job (jobid=95) for client (server), policy XXXXX, schedule Weekly
03/19/2014 19:50:59 - Info nbjm (pid=4387) requesting STANDARD_RESOURCE resources from RB for backup job (jobid=95, request id:{698D1D60-AF97-11E3-A774-41B676056D83})
03/19/2014 19:50:59 - requesting resource XXXXXXXX
03/19/2014 19:50:59 - requesting resource (server).NBU_CLIENT.MAXJOBS.(server)
03/19/2014 19:50:59 - requesting resource (server).NBU_POLICY.MAXJOBS.XXXX
03/19/2014 19:50:59 - granted resource  (server).NBU_CLIENT.MAXJOBS.(server)
03/19/2014 19:50:59 - granted resource  (server).NBU_POLICY.MAXJOBS.XXXX
03/19/2014 19:50:59 - granted resource  MediaID=@aaaab;DiskVolume=nbu01;DiskPool=dd01_nbu01;Path=nbu01;StorageServer=xxxx;MediaServer=(server)
03/19/2014 19:50:59 - granted resource  XXXXXXX
03/19/2014 19:51:00 - estimated 0 kbytes needed
03/19/2014 19:51:00 - begin Parent Job
03/19/2014 19:51:00 - begin VMware: Start Notify Script
03/19/2014 19:51:00 - Info RUNCMD (pid=12611) started
03/19/2014 19:51:00 - Info RUNCMD (pid=12611) exiting with status: 0
Operation Status: 0
03/19/2014 19:51:00 - end VMware: Start Notify Script; elapsed time 0:00:00
03/19/2014 19:51:00 - begin VMware: Step By Condition
Operation Status: 0
03/19/2014 19:51:00 - end VMware: Step By Condition; elapsed time 0:00:00
03/19/2014 19:51:00 - begin VMware: Read File List
Operation Status: 0
03/19/2014 19:51:00 - end VMware: Read File List; elapsed time 0:00:00
03/19/2014 19:51:00 - begin VMware: Create Snapshot
03/19/2014 19:51:01 - started process bpbrm (pid=11174)
03/19/2014 19:51:02 - Info bpbrm (pid=11174) (server) is the host to backup data from
03/19/2014 19:51:02 - Info bpbrm (pid=11174) reading file list for client
03/19/2014 19:51:02 - Info bpbrm (pid=11174) start bpfis on client
03/19/2014 19:51:03 - Info bpbrm (pid=11174) Starting create snapshot processing
03/19/2014 19:51:03 - Info bpfis (pid=11180) Backup started
03/19/2014 19:51:06 - snapshot backup of client (server) using method VMware_v2
03/19/2014 20:02:20 - end VMware: Create Snapshot; elapsed time 0:11:20
03/19/2014 20:02:20 - Info bpfis (pid=11180) done. status: 0
03/19/2014 20:02:20 - Info bpfis (pid=11180) done. status: 0: the requested operation was successfully completed
03/19/2014 20:02:20 - end writing
Operation Status: 0
03/19/2014 20:02:20 - end Parent Job; elapsed time 0:11:20
03/19/2014 20:02:20 - Info nbjm (pid=4387) snapshotid=(server)_1395255059
03/19/2014 20:02:20 - begin VMware: Policy Execution Manager Preprocessed
Operation Status: 0
03/19/2014 20:20:01 - end VMware: Policy Execution Manager Preprocessed; elapsed time 0:17:41
03/19/2014 20:20:01 - begin VMware: Validate Image
Operation Status: 0
03/19/2014 20:20:01 - end VMware: Validate Image; elapsed time 0:00:00
03/19/2014 20:20:01 - begin VMware: Delete Snapshot
03/19/2014 20:20:03 - started process bpbrm (pid=11833)
03/19/2014 20:20:04 - Info bpbrm (pid=11833) Starting delete snapshot processing
03/19/2014 20:20:05 - Info bpfis (pid=11837) Backup started
03/19/2014 20:20:08 - Info bpbrm (pid=11833) INF - vmwareLogger: RegisterExtensionAPI: SYM_VMC_ERROR:  SOAP_ERROR
03/19/2014 20:20:08 - Info bpbrm (pid=11833) INF - vmwareLogger: SOAP 1.1 fault: "":ServerFaultCode [no subcode]
03/19/2014 20:20:08 - Info bpbrm (pid=11833) INF - vmwareLogger: ObjCustomFieldOpAPI: SYM_VMC_ERROR:  SOAP_ERROR
03/19/2014 20:20:08 - Info bpbrm (pid=11833) INF - vmwareLogger: SOAP 1.1 fault: "":ServerFaultCode [no subcode]
03/19/2014 20:32:36 - Critical bpbrm (pid=11833) from client (server): VMware_thaw: Unable to unlock virtual machine: (server)
03/19/2014 20:32:36 - Critical bpbrm (pid=11833) from client (server): vfm_thaw: method: VMware_v2, type: FIM, function: VMware_v2_thaw
03/19/2014 20:32:36 - Critical bpbrm (pid=11833) from client (server): snapshot delete returned status 1
03/19/2014 20:32:36 - Info bpfis (pid=11837) done. status: 1
03/19/2014 20:32:36 - end VMware: Delete Snapshot; elapsed time 0:12:35
03/19/2014 20:32:36 - Info bpfis (pid=11837) done. status: 1: the requested operation was partially successful
03/19/2014 20:32:36 - end writing
Operation Status: 1
Operation Status: 1
the requested operation was partially successful  (1)

Thanks in advance for your help.