Jquery 1.5 ajax调用在处理程序中为webmethod提供无效参数

我在http处理程序中调用webmethod时遇到了问题。jquery.js文件在某个随机位置打开，并提示"无效参数"

代码如下:

JS:

var src = "MyHandler.axd";
var id = "1234566";
$.ajax({
    type: "GET",
    contentType: "application/json; charset=utf-8",
    url: src + "/MyMethod?key=" + id,                
    success: function (msgObj) {
        var msg = msgObj.d;            
    },
    error: function (e) {
        alert("Error");
    }
});

c#

[System.Web.Services.WebMethod(EnableSession = true)]
    [System.Web.Script.Services.ScriptMethod(UseHttpGet = true, ResponseFormat = ResponseFormat.Json)]
    public static string MyMethod(string key)
    {
        return someLogic;
    }

因此，正在为ajax调用调用ProcessRequest方法。

甚至用以下方法尝试过从c#代码中删除了httpget和responseformat。

JS

$.ajax({
    type: "POST",
    contentType: "application/json; charset=utf-8",
    url: src + "/MyMethod",
    data: "{ 'key':'"+ id +"'}",        
    dataType: "json",
    success: function (msgObj) {
        debugger;
        var msg = msgObj.d;
    },
    error: function (e) {
        debugger;
    }
});