Marne,
It seems that the service you're trying to consume sends its message using MTOM extension (MIME type application/soap+xml is used to transfer SOAP XML in MTOM), but service is just able to understand normal SOAP messages (it doesn't contain MIME parts, only text/xml type in HTTP request).
Maybe this is something worth investigating. Higher versions of Mendix might support these webservice calls, I think that Mx 5.19+ supports MTOM, but not sure if this type of message can be handled, but might be worth a try.
Re-importing the WSDL seemed to do the trick.