Unknown web method. Parameter name: methodName

user_1326923 0
Viewed 41205

In researching this problem most SO issues were about the static method as a fix.

Since it's not working with the real (and a bit sophisticated) WebMethod I've just created a simple one for the sake of checking if reaching the method itself is possible.

[WebMethod]
[ScriptMethod(UseHttpGet = false)]
public static string HelloWorld()
{
    return "Hello World!";
}

The call.

<script>
    $(document).ready(function () {
        $.ajax({
            type: "POST",
            contentType: "application/json; charset=utf-8",
            url: "usersWebMethods.aspx/HelloWorld",
            dataType: "json",
            success: function (data) {
                alert(data.d);
            }
        });
   });
</script>

It always comes down to 500 (Internal Server Error)

Unknown web method HelloWorld.
Parameter name: methodName
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 
Exception Details: System.ArgumentException: Unknown web method HelloWorld.
Parameter name: methodName

Why is this failing?

pagemethods asp.net ajax c#
6 Answers

Missing the [WebMethod] above your server side function will also cause this error.

user_18150100

To be honest, I've just realised "again" how tired we could be in some cases.

For me it was just a private method instead of a public one.

user_6294700

In my case there was a problem in the URL, it was a Asp.Net Website application:

For ex:

$.ajax({
 type: "POST",
 contentType: "application/json; charset=utf-8",
 url: "usersWebMethods.aspx/HelloWorld",  <----- Here 
 dataType: "json",
 success: function (data) {
    alert(data.d);
 }
});

My usersWebMethods.aspx in inside UI (Custom Created) folder so If I put URL as usersWebMethods.aspx/HelloWorld it does not work but when I added leading / to it then ajax method called properly!

Changed from:

usersWebMethods.aspx/HelloWorld

To 

/usersWebMethods.aspx/HelloWorld  --
user_71247610
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