从Jquery调用ASP服务

I am trying to set up a simple service that accepts a string and returns a string. I have the ASP.net code built and working with it's built in test page, but cant seem to call the service from jquery.

ASP:

<System.Web.Script.Services.ScriptService()> _
<System.Web.Services.WebService(Namespace:="https://domain/decode")> _
<System.Web.Services.WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<ToolboxItem(False)> _
Public Class Decode
    Inherits System.Web.Services.WebService

    <WebMethod()> _
    Public Function Decode(Image64 As String) As String

        Dim Code As String = "test"
        Return Code
    End Function

End Class

Then I am trying to call this service from jquery on an existing php page:

<script src="js/jquery-1.9.1.js"></script>
<script language="javascript" type="text/javascript">
$(function() {

           $.ajax({
               type: "POST",
               url: "https://domain/decode/decode.asmx/Decode",
               data: {Image64: ""},
               contentType: "application/json; charset=utf-8",
               dataType: "json",
               success: OnSuccess,
               error: OnError

       });
 });
       function OnSuccess(data, status)
       {
          alert(data.d);
       }

       function OnError(request, status, error)
       {
           alert(request.statusText);
       }

I have tried changing the data format data: "{}" etc and I keep getting "Internal Server Error" back.

I assume something might be wrong on the ASP side as I am completely new to that, but cant figure out what...

Well, not working with native, but found a great SOAP plugin: https://github.com/doedje/jquery.soap

Now its working fine =)