Hi
the unsupported OS also doesn't explain this quite unusual error in the log. Can you upload the worker log, too? It seems in this case Converter didn't include it in the bundle and you should get it manually. It can be found in "%ALLUSERSPROFILE%\Application Data\VMware\VMware vCenter Converter Standalone\logs", look for vmware-worker-###.log and get the one that is from the time of this mishap.
Regards,
Plamen