Invalid postback or callback argument. Event validation is enabled using '<pages enableEventValidation="true"/>'

The problem is that ASP.NET does not get to know about this extra or removed listitem. You got an number of options (listed below):

• Disable eventvalidation (bad idea, because you lose a little of security that come with very little cost).
• Use ASP.NET Ajax UpdatePanel. (Put the listbox in the Updatepanel and trigger a update, if you add or remove listbox. This way viewstate and related fields get updates and eventvalidation will pass.)
• Forget client-side and use the classic postback and add or remove the listitems server-side.

I hope this helps.

I had an experience with DataGrid. One of it's columns was "Select" button. When I was clicking "Select" button of any row I had received this error message:

"Invalid postback or callback argument. Event validation is enabled using in configuration or <%@ Page EnableEventValidation="true" %> in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation."

I changed several codes, and finally I succeeded. My experience route:

1) I changed page attribute to EnableEventValidation="false". But it didn't work. (not only is this dangerous for security reason, my event handler wasn't called: void Grid_SelectedIndexChanged(object sender, EventArgs e)

2) I implemented ClientScript.RegisterForEventValidation in Render method. But it didn't work.

protected override void Render(HtmlTextWriter writer)
{
    foreach (DataGridItem item in this.Grid.Items)
    {
        Page.ClientScript.RegisterForEventValidation(item.UniqueID);
        foreach (TableCell cell in (item as TableRow).Cells)
        {
            Page.ClientScript.RegisterForEventValidation(cell.UniqueID);
            foreach (System.Web.UI.Control control in cell.Controls)
            {
                if (control is Button)
                    Page.ClientScript.RegisterForEventValidation(control.UniqueID);
            }
        }
    }
}

3) I changed my button type in grid column from PushButton to LinkButton. It worked! ("ButtonType="LinkButton"). I think if you can change your button to other controls like "LinkButton" in other cases, it would work properly.

You are really going to want to do 2 or 3, don't disable event validation.

There are two main problems with adding items to an asp:listbox client side.

• The first is that it interferes with event validation. What came back to the server is not what it sent down.

• The second is that even if you disable event validation, when your page gets posted back the items in the listbox will be rebuilt from the viewstate, so any changes you made on the client are lost. The reason for this is that a asp.net does not expect the contents of a listbox to be modified on the client, it only expects a selection to be made, so it discards any changes you might have made.

The best option is most likely to use an update panel as has been recommended. Another option, if you really need to do this client side, is to use a plain old <select> instead of an <asp:ListBox>, and to keep your list of items in a hidden field. When the page renders on the client you can populate it from a split of your text field contents.

Then, when you are ready to post it, you repopulate the hidden field's contents from your modified <select>. Then, of course, you have to split that again on the server and do something with your items, since your select is empty now that it's back on the server.

All in all it's a pretty cumbersome solution that I would not really recommend, but if you really have to do client-side modifications of a listBox, it does work. I would really recommend you look into an updatePanel before going this route, however.

If you fill the DropdownList through client side script then clear the list before submit the form back to server; then ASP.NET will not complain and the security will be still on.

And to get the data selected from the DDL, you can attach an "OnChange" event to the DDL to collect the value in a hidden Input or in a textbox with Style="display: none;"

3: I changed my button type in grid column from "PushButton" to "LinkButton". It worked! ("ButtonType="LinkButton") I think if you can change your button to other controls like "LinkButton" in other cases, it would work properly.

I wish I could vote you up, Amir (alas my rep is too low.) I was just having this problem and changing this worked like a champ on my gridview. Just a little aside, I think the valid code is: ButtonType="Link"

I suspect this is because when you click 'edit', your edit changes to 'update' and 'cancel' which then change back to 'edit' on submit. And these shifting controls make .net uneasy.

Ajax UpdatePanel makes it, and I think it's the easiest way, ignoring the Ajax postback overhead.

In this case add id to the button in RowDataBound of the grid. It will solve your problem.

A simple solution for this problem is to use the IsPostBack check on your page load. That will solve this problem.

We ran into this same issue when we were converting our regular ASPX pages to Content pages.

The page with this issue had a </form> tag within one of the Content sections, thus two form end tags were rendered at run time which caused this issue. Removing the extra form end tag from the page resolved this issue.

I was using datalist and I was getting the same error for my push button. I just use IsPostBack to check and fill my controls and the problem is solved! Great!!!

For us the problem was happening randomly only in the production environment. The RegisterForEventValidation did nothing for us.

Finally, we figured out that the web farm in which the asp.net app was running, two IIS servers had different .net versions installed. So it appears they had different rules for encrypting the asp.net validation hash. Updating them solved most of the problem.

Also, we configured the machineKey(compatibilityMode) (the same in both servers), httpRuntime(targetFramework), ValidationSettings:UnobtrusiveValidationMode, pages(renderAllHiddenFieldsAtTopOfForm) in the web.config of both servers.

We used this site to generate the key https://www.allkeysgenerator.com/Random/ASP-Net-MachineKey-Generator.aspx

We spent a lot of time solving this, I hope this helps somebody.

<appSettings>
   <add key="ValidationSettings:UnobtrusiveValidationMode" value="None" />
...
</appSettings>
<system.web>
   <machineKey compatibilityMode="Framework45" decryptionKey="somekey" validationKey="otherkey" validation="SHA1" decryption="AES />
   <pages [...] controlRenderingCompatibilityVersion="4.0" enableEventValidation="true" renderAllHiddenFieldsAtTopOfForm="true" />
   <httpRuntime [...] requestValidationMode="2.0" targetFramework="4.5" />
...
</system.web>

I worked around this exact error by not adding the ListBox to a parent Page/Control Controls collection. Because I really didn't need any server-side functionality out of it. I just wanted to use it to output the HTML for a custom server control, which I did in the OnRender event handler myself. I hoped that using the control would save me from writing to the response my own html.

This solution probably won't work for most, but it keeps ASP.NET from performing the ValidateEvent against the control, because the control doesn't retain in memory between postbacks.

Also, my error was specifically caused by the selected list item being an item that wasn't in the listbox the previous postback. Incase that helps anyone.

I had the same problem, two list boxes and two buttons.

The data in the list boxes was being loaded from a database and you could move items between boxes by clicking the buttons.

I was getting an invalid postback.

turns out that it was the data had carriage return line feeds in it which you cannot see when displayed in the list box.

worked fine in every browser except IE 10 and IE 11.

Remove the carriage return line feeds and all works fine.

My problem was solved when cancel event at end of grid event at server side.

protected void grdEducation_RowEditing(object sender, GridViewEditEventArgs e)
{
  // do your processing ...

  // at end<br />
  e.Cancel = true;
}