Move-VM - 'Incorrect function.'('0x80070001').

Hi

I am trying to live migrate a Hyper-V Guest between 2 Server 2012 Machines using the following powershell command:-

Move-VM vm server Hyper-v Host 2 –IncludeStorage –DestinationStoragePath f:\temp

(names have been changes)

but after the first 2 vhdx files have been copied it fails each time (tried 3 times) with the following error:

Move-VM : Virtual machine migration operation for 'VM Server' failed at migration source 'Hyper-V Host 1'. (Virtual machine ID
99E5A55E-B653-4F1E-9E50-77F96A90F37F) Migration did not succeed. Mirror operation failed for the source VHD file
'F:\hyper-v\vhd\VM Server-F_Drive.vhdx' to the destination file \\Hyper-V Host 2\Hyper-V Host 1.113901622$\f\temp\Virtual Hard Disks\VM Server-F_Drive.vhdx': 'Incorrect function.'('0x80070001').

Anyone seen this before?