POST request using WWW class. error: necessary data rewind wasn't possible

I'm trying to call a web service, using the WWW class with a WWWForm to fill in the POST data.

It's an extremely simple web service for this test purpose. All it does is take in two ints, sum them and return the result. Unfortunately, when I call the service I get this error when it returns:

"necessary data rewind wasn't possible"

Does anybody have any idea what the cause of this could be?

Here is my code snippet for the request. It's really just this simple a test:

     WWWForm form = new WWWForm();
     
     form.AddField("A", 1);
     form.AddField("B", 1);
     
     WWW request;
     
     request = new WWW(url, form);

     yield return request;
     
     if (request.error != null)
     {
         Debug.Log("Error completing request: " + request.error);
     }
     else
     {
         Debug.Log(request.text);
     }

Any assistance on this issue would be greatly appreciated.

Thanks in advance.

::EDIT:: - Added server side web method.

     [WebMethod]
     public int AddTest(int A, int B)
     {
         return A + B;
     }

And here is the URL which is stored in the variable url in the request:

 http://www.somedomain.com/SomeDirectory/WebServices.asmx/AddTest