I ran into this issue aswell.
This is how I got around it.
First install the VMware Converter Stand alone client to the server you want to convert.
located here on the Server you installed the stand alone converter on: C:\Program Files (x86)\VMware\VMware vCenter Converter Standalone\VMware-Converter-Agent.exe
Then I ran the converter from the plugin inside the VIC. Everything ran smoothly from there.
Trying to just run the import from the plugin would fail because it would not detect the drives, running the converter from the stand alone client failed with VSS errors.
Jeff