VM-Export fails (somehow not)

For now 2 months I'm getting an error, when I export out biggest VM with about 467 GB.
_Error: Received exception: In die Übertragungsverbindung können keine Daten gesc
hrieben werden: Eine vorhandene Verbindung wurde vom Remotehost geschlossen.
Error: Unable to write output file: D:\VM-Export\VM1.xva
Error: Caught exception: In die Übertragungsverbindung können keine Daten geschr
ieben werden: Eine vorhandene Verbindung wurde vom Remotehost geschlossen.
Starte VM VM1_

Which should be about "Coudn't write data to the transfer(data?)connection" And that it closed the connection to the remotehost.

But my local (backup is done va xe.exe on a backupserver) XenCenter from Dundee TP3 says, that the export was successfully done:

I was also able to impor that VM with the XenCenter to my Dundee TP3 testserver without any problems (note: patch from Marcus Granado applied to push import/export performance) and I was even able to start the VM.
To be sure, I ran a chkdsk /f /r on both VHDs and it didn't report any problems.