ASP.NET Calling WebMethod with jQuery AJAX "401 (Unauthorized)"

In my case the problem was in URL that calls Ajax.asmx this URL was not correct according to a webserver setup, e.g. `"/qa/Handlers/AjaxLib.asmx/"` worked for me instead of `"/Handlers/AjaxLib.asmx/"` (works fine on PROD servers in my particular situation):

$.ajax({
url: '/qa/Handlers/AjaxLib.asmx/' + action,
type: "POST",
async: false,
data: data,
contentType: "application/json; charset=utf-8",
success: function () {

My AJAX was then called out of scope of my IIS virtual application directory "qa", hence Authorization error occured `({"Message":"Authentication failed.","StackTrace":null,"ExceptionType":"System.InvalidOperationException"}).`

You have to comment out only in ~/App_Start/RouteConfig.cs

// settings.AutoRedirectMode = RedirectMode.Permanent;

(Or do this)

settings.AutoRedirectMode = RedirectMode.Off;

There is nothing to do with Authentication in Web.config file.

To allow this Web Service to be called from script, using ASP.NET AJAX. Add the following attribute to the class

[System.Web.Script.Services.ScriptService]


I faced similar issue and the adding this attribute resolved it.

For me, I had an invalid "data:" parameter in my JQuery Ajax call. But rather than either .NET or JQuery complaining about the the parameter values, I was (misleadingly in my opinion) getting the 401 Unauthorized error.