ACS 4.2.1(XenServer 6.1) VM suspended on Live Migration

[ry...@hitachi-solutions.com]

Hi,
Recently I did "Live Migration" on XenServer 6.1 and CloudStack4.2.1.

"Live Migration" occured Exception,
And the VM became "suspend" status.

The CloudStack management-server.log was

~~~~
Unable to migrate VM(i-5-28-VM) from host(UUID) due to Task failed!
            uuid:UUID
       nameLabel:Async.VM.pool_migrate
 nameDescription:
allowedOperation:[]
currentOperation:{}
         created:Mon May 25 11:21:24 JST 2015
        finished:Mon May 25 11:24:23 JST 2015
          status:failure
      residentOn:com.xensource.xenapi.Host@xxxxx
        progress:1.0
            type:<none/>
          result:
       errorInfo:[INTERNAL_ERROR, File "xapi_xenops.ml", line 1806, characters 3-9:Assertion failed]
     otherConfig:{debug_info:cancel_points_seen=17}
       subtaskOf:com.xensource.xenapi.Task@xxxxxx
        subtasks:[]
~~~~


The XenServer SMlog was

~~~~
*** vdi_activate : EXCEPTION util.SMException, VDI <uuid> locked
     File "/opt/xensource/sm/SRCommand.py", line  96, in run
         return self._run_locked(sr)
     File "/opt/xensource/sm/SRCommand.py", line 143, in run
         return self._run(sr, target)
     File "/opt/xensource/sm/SRCommand.py", line 238, in run
         writable, caching_params)
     File "/opt/xensource/sm/blktap2.py", line 1413, in run
         raise util.SMException("VDI %s locked" % vdi_uuid)
......

Raising exception [46, The VDI is not available [opterr=VDI <uuid> locked]]
~~~~

The VM was DB Server, And it is always available.
But, Other VMs(Web Server etc) had been able to successfully migrated.

Please teach me this Problem!

Thanks,
Ryota