Hi Will,
ARGUMENT NOT FOUND refers to SSL error. Are there any imported schemas in the WSDL file located on a HTTPS server? You can see that by opening the file in a text or XML editor: <xsd:import location="https://...">
If that's the case, download these files in a browser (check if they have further referenced files as well). Once all files are downloaded, update the references to relative URI (remove http://... just leave .xsd in the reference) and place everything in one folder.
You can also create a monolithic WSDL from these, see SAP KBA 2200995.
Cheers,
Attila