Question

How to clear the following error:

Only one instance of a ScriptManager
can be added to the page.
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.InvalidOperationException: Only
one instance of a ScriptManager can be
added to the page.

Source Error: An unhandled exception
was generated during the execution of
the current web request.
Information regarding the origin and
location of the exception can be
identified using the exception stack
trace below.

The following is my html Markup:

<%@ Page Language="C#" AutoEventWireup="true" MasterPageFile="~/MasterPage.master"   
    CodeFile="ManualReport.aspx.cs" Inherits="ManualReport" %>
<%@ Register assembly="Telerik.Web.UI" namespace="Telerik.Web.UI" 
    tagprefix="telerik" %>

<asp:Content  ContentPlaceHolderID="ContentPlaceHolder1" runat="server" 
    ID="ContentPlaceHolder1">

<%@ Register Assembly="Microsoft.ReportViewer.WebForms, Version=9.0.0.0, 
    Culture=neutral,   PublicKeyToken=b03f5f7f11d50a3a"
    Namespace="Microsoft.Reporting.WebForms" TagPrefix="rsweb" %>

<form id="mainform" runat="server"><table width="100%" >
    <asp:ScriptManager ID="ScriptManager2" runat="server">
    </asp:ScriptManager>

    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>

</form>

    <div>
         <tr><td>Customer Name</td><td>
        <asp:RadioButton ID="rdbcustomerAll" runat="server"  Visible ="false"   
 GroupName="CustomerValidation" 
                 Text="All" Checked="false" /></td><td>
             <asp:RadioButton ID="rdbcustomerSpecific" runat="server"  
  GroupName="CustomerValidation" Visible="false" Text="Spec" Checked="true" /></td></
  td><td>
                     <asp:DropDownList ID="cmbName" runat="server">
                     </asp:DropDownList></td></tr>
                     <tr><td>Date</td><td><asp:RadioButton ID="rdbDateAll" runat="server" 
  Visible ="false" GroupName="DateValidation" 
                 Text="All"  /></td><td>
             <asp:RadioButton ID="rdbDateSpec" runat="server" Visible ="false" Checked="true" GroupName="DateValidation" Text="Spec" /></td><td>
        <telerik:RadDatePicker ID="rdpDate" runat="server" xmlns:telerik="telerik.web.ui">
                              </telerik:RadDatePicker>
                     </td></tr>

Answer 1

Why did you add the ScriptManager two times on your page? You can only add one, and that’s what the error says. Only one ScriptManager instance is allowed per page.

Please remove the ScriptManager2 and it will work for you.

Secondly ScriptManger should be under Form Tag. like..

<form id="mainform" runat="server"><table width="100%" >

  <asp:ScriptManager ID="ScriptManager1" runat="server">
  </asp:ScriptManager>

</form>