Hi Wolfgang,
It’s hard to answer your question regarding the web service method without knowing what the signature of that service looks like. Can you browse to the URL of that service and see what the WSDL looks like? If you can, you should be able to find out if the method accepts parameters or not. Also, do you have a test harness to make sure that the service is working properly? Have you tried consuming this web service in a simple .NET application?
Daniel.