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Editorial Team
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Asked: 2026-05-13T07:24:11+00:00

I have problem with my UserControl. It has inside the UpdatePanel, but it must

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I have problem with my UserControl. It has inside the UpdatePanel, but it must be placed inside the tag to get worked (otherwise, the PostBack is not asynchronous)

The problem is, if I put that UserControl in e.g. Default.aspx page, the error appears
“A page can have only one server-side Form tag”

how to cope with that ?

[edit]

the UserControl.ascx code:

 <%@ Control Language="C#" AutoEventWireup="true" CodeBehind="PodmiotyZwolnioneCtrl.ascx.cs" Inherits="FormularzPodatkowy.PodmiotyZwolnioneCtrl" %>
 <%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="ajax" %>

<link href="AjaxStyle.css" rel="stylesheet" type="text/css" />

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >

<body>
<form id="form1" runat="server">
<div>
        <asp:UpdatePanel ID="UpdatePanel1" 
                         UpdateMode="Conditional"
                         runat="server">
            <ContentTemplate>
               <fieldset>
               <legend>UpdatePanel content</legend>
                <!-- Other content in the panel. -->
                <%=DateTime.Now.ToString() %>
                <br />
                <asp:Button ID="Button1" 
                            Text="Refresh Panel" 
                            runat="server" />
                </fieldset>
            </ContentTemplate>
        </asp:UpdatePanel>
    </div>
</form>
</body>
</html>

the WebForm1.aspx code:

 <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="FormularzPodatkowy.WebForm1" %>

 <%@ Register src="PodmiotyZwolnioneCtrl.ascx" tagname="PodmiotyZwolnioneCtrl" tagprefix="uc1" %>

 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
    <asp:ScriptManager ID="ScriptManager1" runat="server" />
    <uc1:PodmiotyZwolnioneCtrl ID="PodmiotyZwolnioneCtrl1" runat="server" />
</form>
 </body>
</html>
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1 Answer

  1. Editorial Team

    Your code should be:

    <%@ Control Language="C#" AutoEventWireup="true" CodeBehind="PodmiotyZwolnioneCtrl.ascx.cs" Inherits="FormularzPodatkowy.PodmiotyZwolnioneCtrl" %>
 <%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="ajax" %>

<link href="AjaxStyle.css" rel="stylesheet" type="text/css" />

<div>
        <asp:UpdatePanel ID="UpdatePanel1" 
                         UpdateMode="Conditional"
                         runat="server">
            <ContentTemplate>
               <fieldset>
               <legend>UpdatePanel content</legend>
                <!-- Other content in the panel. -->
                <%=DateTime.Now.ToString() %>
                <br />
                <asp:Button ID="Button1" 
                            Text="Refresh Panel" 
                            runat="server" />
                </fieldset>
            </ContentTemplate>
        </asp:UpdatePanel>
    </div>

    It looks like you converted a page to a control and forgot to remove the page-specific elements

    Also, if your postbacks are not asynchronous, look at your web.config for:

        <xhtmlConformance mode="Legacy"/>

    and change it to:

        <xhtmlConformance mode="Transitional"/>

    I just spent three days at work finding that solution to UpdatePanel always posting back to the server.

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