use your webbrowser to visit the webservice url there you should be able to see a list of its functions together with a testing form. What kind of (data)types are you using? Only the basic ones work out of the box so you might also want to take a look at the generated source you use to connect to the webservice. Hope this is of some help.

E.g. have a look at the babelcode webservice: http://lingua.embarcadero.com/babelcode/converter.asmx