Unknown web method. Parameter name: methodName

Question

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?

maybe I got it all wrong or I haven't explained myself properly. This is just an .aspx page using webmethods in the codebehind. It's not a webservice. — Daniel Sh.
– Daniel Sh., Commented Dec 22, 2013 at 23:38
Ah ok, are you using a ScriptManager? If so do you have the EnableScriptMethods enabled? — James
– James, Commented Dec 22, 2013 at 23:49
No, just using jQuery, I was sure there's no need to use a ScriptManager — Daniel Sh.
– Daniel Sh., Commented Dec 22, 2013 at 23:56
As embarrassing as it is to admit this, my problem was because the method's access modifier was private instead of public.... — JWiley
– JWiley, Commented Aug 17, 2015 at 12:54

ΩmegaMan · Accepted Answer · 2017-06-28 13:19:07Z

77

I had this issue as well, but slightly differently I had this method in a .asmx file and so ran across the "static" issue, but in a different way.

If you have a method as part of your Page class, it must be static.

If you've put a method in an .asmx file to use across several pages, it must not be static.

edited Jun 28, 2017 at 13:19

ΩmegaMan

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answered Jun 17, 2014 at 10:46

Rob

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3 Comments

Mohammed Dawood Ansari Over a year ago

I got the same issue while using WebMethod in ASP .NET Page, just made it static and it started working. +1

GoldBishop Over a year ago

converted a page member method to a webmethod and forgot to change scope and member attribute....

Lukas Over a year ago

I can't believe that worked! In my asmx page I had a public static method. After removing the static the method was hit successfully! Thank you!

ΩmegaMan · Accepted Answer · 2019-02-22 14:18:23Z

22

I had a problem in the actual .aspx file, the line

<%@ Page Language="C#" 
         AutoEventWireup="true" 
         CodeBehind="xxx.xxx.cs" Inherits="xxx.xxx" %>

wasn't present in the code. How did it get changed? I Don't know :(.

edited Feb 22, 2019 at 14:18

ΩmegaMan

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answered Dec 24, 2013 at 12:55

Daniel Sh.

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5 Comments

InGeek Over a year ago

wahahhahhah thanks sooooooooooooooooooooooooooooo much. exactly silly spent 3 hours on it

Daniel Sh. Over a year ago

@INgeeg glad I was of help :)

LacOniC Over a year ago

What was the problem in .aspx page?

msulis Over a year ago

thanks for admitting it here for those of us who were suffering the same sad situation!

Daniel Sh. Over a year ago

@LacOniC the line <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="xxx.xxx.cs" Inherits="xxx.xxx" %> was mistakenly erased from the page. Added it and it worked.

ΩmegaMan · Accepted Answer · 2017-06-23 18:41:39Z

3

For me, the primary issues was to change javascript post to pass in no arguments such as

$http.post("Status.aspx/MyData", {})

Then to verify nothing was cached, I then deleted [System.Web.Services.WebMethod] in the code behind file above public static string MyData(). Then I built the project to failure, then re-added the aformentioned deleted attribute and built to success.

Upon running it worked.

edited Jun 23, 2017 at 18:41

answered Jun 9, 2017 at 19:38

ΩmegaMan

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1 Comment

NickG Over a year ago

The second part of this worked for me. It was some kind of stupid caching issue. Rename the function by adding "2" to the end (client-side and server side) and it worked! Renamed it back to the original name: STILL working, despite the code now being byte-identical to when it didn't work. And I'd already cleaned out Temporary ASP.NET Files so god knows where it was being cached... (RAM?)

ΩmegaMan · Accepted Answer · 2019-02-22 14:18:54Z

3

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

edited Feb 22, 2019 at 14:18

ΩmegaMan

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answered Feb 2, 2018 at 21:57

hogarth45

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1 Comment

John Baker Over a year ago

I've done this a hundred times, and I always forget the attribute. Thanks!

ΩmegaMan · Accepted Answer · 2019-02-22 14:19:21Z

3

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.

edited Feb 22, 2019 at 14:19

ΩmegaMan

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answered Aug 31, 2018 at 11:36

smlnl

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1 Comment

Protector one Over a year ago

Yes, very tired. Same goes for protected methods.

Aman Attari · Accepted Answer · 2023-05-10 07:30:11Z

So the cases may have below based on the answers.

1) check refrence of the code behind page in the top of aspx file <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="xxx.xxx.cs" Inherits="xxx.xxx" %>
2) $http.post("Status.aspx/MyData", {}) forgot to pass the argument and the argument name should be same in client side code(jquery) and aspx.cs method
3) forgot to put [WebMethod] just above the method which comes under System.Web.Services;
4) forgot to use public access specifier
5) forgot to use static keyword in method
6) forgot to compile the code after adding method in running project.

Adding one more case number 6 if some body forgot to compile the code after adding the web method in aspx.cs file.

Prashant Pimpale · Accepted Answer · 2019-09-21 09:36:50Z

0

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  --

answered Sep 21, 2019 at 9:36

Prashant Pimpale

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Comments

Abdi fatah · Accepted Answer · 2023-03-05 07:28:50Z

0

I run into this exact problem in ASP.net(framework/web forms) with JS using webservice and I solved it by removing the static key word from the method declaration

 [WebMethod]
 public List<ViewModel> HelloWorld()
 {
   //Code goes here
 }

instead of

 [WebMethod]
 public static List<ViewModel> HelloWorld()
 {
   //Code goes here
 }

edited Mar 5, 2023 at 7:28

answered Nov 16, 2022 at 20:35

Abdi fatah

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