Large thin-provisioned VMDKs won't copy f/ Pro 4 to ESXi 5.5

We are using a ReadyNAS Pro 4 as off-line backup of VMs and to move VMs between 2 sites. Running RAIDiator 4.2.26 and ESXi 5.5. Using NFS. We copied a bunch of VMs to the NAS at site 1. Sent it to site 2. Using Datastore Browser in VMWare we can copy anything off the NAS to ESXi's direct attached storage EXCEPT thin-provisioned VMDKs of 2 VMs that are thin provisioned at 524GB. (The used space is no where close to that - more like 43 gig) The error message is uninformative. I can't get into the system right now to copy the exact wording because of a network issue. :? But when we try the copy it processes for a few seconds and then throws an error like "Operation failed because of file...". Nothing in the ReadyNAS log. Same generic error in ESXi.

Hopefully someone knows the fix?

MORE INFO: Here is the error from VMWare log.

[ :ShowErr :M: 6] 2014-09-15 08:15:12.568 Error: Error caused by file [DST_Share (2)] Louisville Redneck/DSLBIG/MTG-WWW1/MTG-WWW1.vmdk
Stack Trace:
at VirtualInfrastructure.Utils.Log.Trace(String, String, TraceType)
at VpxClientCommon.Util.Dialogs.Trace(String, String, String, TraceType)
at VpxClientCommon.Util.Dialogs.ShowError(IWin32Window, String, String)
at VpxClientCommon.DatastoreBrowserClient.FileTransferProgressBar.EnterCompletionState(String)
at VpxClientCommon.DatastoreBrowserClient.FileTransferProgressBar.OnTaskComplete(TaskMonitor)
at VpxClientCommon.TaskMonitor.ProcessFilterUpdates(FilterUpdate)
at VpxClientCommon.TaskMonitor.OnUpdates(FilterUpdateArray)
at VirtualInfrastructure.Updates.PollerDispatcherImpl.NotifyUpdates(Map`2)
at VirtualInfrastructure.Updates.PollerDispatcherImpl.<ProcessUpdates>b__2(Object)
...
at System.Windows.Forms.Application.Run()