I had the same problem and Mendix let me know it was because of the <service> tag was not in the WSDL.
This was what I did to fix it, maybe it works in your case to. Otherwise upload your WSDL so we can look into it.
<service name="x"> <port name="x" binding="y"> <soap:address location="http://localhost:8080/ws/Published_web_service/"/> </port> </service>