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Asked: 2026-05-26T09:49:01+00:00

I have a Web Content Form containing a Div and various Server controls like

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I have a Web Content Form containing a Div and various Server controls like DropDownList. When I run the application, it runs well without any errors, but when I view the HTML source, the Server controls are red underlined. On bringing the mouse over, say, DropDownList, a tooltip warning is displayed:

DropDownList is not a known element. This can occur if there is a compilation error in a website.

Edited

<%@ Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="contentReportSchemesMenu.aspx.cs" Inherits="contentReportMenu" Title="Reports Menu" %>

<asp:Content ID="ContentReportMenu" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
    <div id="divMenu" class="divMenu" runat="server">
        <table id="tblMenuLayout" class="Options" runat="server">
        <tr>
            <td colspan="2" class="Top">Scheme Reports Menu</td>
            <td></td>
        </tr>
            <tr>
                <td class="Left">Report Type</td>
                <td class="Right">
                        &nbsp;<asp:DropDownList ID="ddlReportType" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddlReportType_SelectedIndexChanged"></asp:DropDownList>
                </td>
            </tr>        
            <tr>
                <td class="Left">Select District</td>
                <td class="Right">
                        &nbsp;<asp:DropDownList ID="ddlDistrict" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddlDistrict_SelectedIndexChanged" Enabled="False"></asp:DropDownList>
                </td>
            </tr>
            <tr>
                <td class="Left">Select Block</td>
                <td class="Right">
                    &nbsp;<asp:DropDownList ID="ddlBlock" runat="server" AutoPostBack="true" Enabled="False" OnSelectedIndexChanged="ddlBlock_SelectedIndexChanged"></asp:DropDownList>
                </td>
            </tr>
            <tr>
                <td colspan="2" style="text-align:center">
                    <asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" Enabled="False" />
                    &nbsp;</td>
                <td></td>
            </tr>
        </table>
    </div>
</asp:Content>
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1 Answer

  1. Editorial Team

    A quick Google search soon found the solution: Delete the files from “C:\Documents and Settings[Username]\Application Data\Microsoft\VisualStudio\9.0\ReflectedSchemas” folder (or “…\VisualStudio\8.0\…” if running Visual Studio 2005) in Windows XP. In Windows 7 it is under “C:\Users{User Profile}\AppData\Roaming\Microsoft…etc”. Remember also the “VisualStudio” part of the path will be different depending on the version installed.

    I closed Visual Studio (always a good ideas for changes that will affect the IDE), deleted the files then re-opened the project. The warnings were gone.

    I found references to this solution at:
    http://forums.asp.net/t/1205528.aspx
    http://blogs.msdn.com/mikhailarkhipov/archive/2005/04/21/410557.aspx

    FYI, the search term I used in Google was “element is not supported”.

    I don’t know why this happens but I do know there are some flakey domain profile things happening in the network environmnet.

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