It’s an error caused when VDP cannot introspect the WS source. This can happen On Denodo Web Design Studio, when you have a combination of wrong WSDL (incorrect host or port) and authentication method (e.g., HTTP Basic or HTTP SPNEGO) in combination. Please consider verifying the input fields on your connection tab under configuration. You can get more details on the error from the logs located at <DENODO-HOME>\logs\design-studio.
If the issue persists and you have a valid Support account, I would request that you open a support case where the Support Team can assist you.
Hope this helps!