ajax POST to MS Webservice

ajax POST to MS Webservice

Hi,
i have a problem.
I have an ajax call to a webservice, and it works.
Now I try to set parameters, and it donsn't work anymore.
I try it with parameters in data and without.
The Webservice will only be called, if the webservice has no parameters.
I have testet the webservice in the visual studio (2005), and it works.

Can anyone help me?

$("input.ajaxbtnPlanAdminFreigabe").click(function(){          
                $.ajax({
                 type: "POST"
                ,contentType: "application/json; charset=utf-8"
                ,url: "WebService/vpt_status.asmx/PlanAdminFreigabe"
                ,data: "{'PcTreeID':'4711','ProduktID':'1004'}"
                //,data: "{}"
                ,dataType: "XML"
                //,cache: false
                ,async: false
                //,beforeSend:
                //,dataFilter:
                ,error: function(returnXML) {             
                         $(returnXML).find('ERROR').each(function(){                
                            alert($(this).text());                                        
                            }); //close each(
                } //close success
                ,success:
                         function(returnXML) {             
                         $(returnXML).find('SUCCESS').each(function(){                
                            alert($(this).text());                                        
                            }); //close each(
                } //close success
                //,complete: function(returnXML){alert(returnXML.text());}                          
                });               
            });


[WebMethod]
        public XmlDocument PlanAdminFreigabe(string PcTreeID, string ProduktID)
        {
            XmlDocument xmlDoc = new XmlDocument();
            XmlNode myRoot, myNode;
           
            myRoot = xmlDoc.CreateElement("XML");
            xmlDoc.AppendChild(myRoot);

            try
            {        
                // Update PlanFreigabe
                DbController db = new DbController();
                db.updatePlanFreigabeAdmin(int.Parse(PcTreeID), int.Parse(ProduktID));
               
                myNode = xmlDoc.CreateElement("SUCCESS");
                myNode.InnerText = "Admin Freigabe ausgeführt.";
                myRoot.AppendChild(myNode);

            }
            catch(Exception)
            {
                myNode = xmlDoc.CreateElement("ERROR");
                myNode.InnerText = "Es ist ein Fehler aufgetreten.";
                myRoot.AppendChild(myNode);
            }

            return xmlDoc;
           
        }