Internal Server Error for an ajax request from Visual Web Part to application page

Question

I have Internal Server Error in response to an Ajax call. The request is sent from a Visual Web Part, inside a solution, towards an application page :

The application page has this method:

 [WebMethod(EnableSession = true)]
        [ScriptMethod(UseHttpGet = true)]
        public static String Creation()
        {
           // do something ...

                return "{\"status\":\"success\"}";

        }

The visual web part makes this JQuery call:

 $.ajax({
                    type: "GET",                    url: "/_layouts/15/PrenCalendarExchange/Registration.aspx/Creation",
                    dataType: 'json',
                    contentType: 'application/json',
                    data: {
                        prenSubject: $('#prenSubject').val()
                        , location: $('#location').val()
                    },
                    error: function (XMLHttpRequest, textStatus, errorThrown) {
                             alert("Error: " + textStatus + " - " + errorThrown);
//INTRNAL SERVER ERROR IS THROWN HERE
                    }
                });

The call works fine in my local environment but fails on a test environment.

Answer 1

I used this syntax and it is working fine:

Application Page:

[System.Web.Services.WebMethod]
public static string myWB()
{
     return "my HTML or JSON"
}

The call from the visual web part is same as yours.
So maybe try to add just [System.Web.Services.WebMethod] to your method.