title: Unrecognized tag prefix or device filter (Visual Studio 2010)
body: <p>I am trying my hands on Visual Studio 2010 (Asp.Net 4.0) for the first time. I want to use Ajax controls, mainly ComboBox control.</p>
  
  <p>I followed the step-by-step procedure mentioned in this <a href="http://weblogs.asp.net/yousefjadallah/archive/2010/04/16/installing-ajax-control-toolkit-4-in-visual-studio-2010.aspx" rel="nofollow">link</a> to download and install AjavControlToolkit.</p>
  
  <p>I also followed this <a href="http://www.asp.net/web-forms/tutorials/ajax-control-toolkit/combobox/how-do-i-use-the-combobox-control-cs" rel="nofollow">link</a> for steps to add ComboBox to my webpage.</p>
  
  <p>But no matter what I do, there is a green line under the control and I'm getting the error "Unrecognized tag prefix or device filter 'ajax'".</p>
  
  <p>My web.config file looks like this:</p>
  
  <pre><code>         &lt;configuration&gt;
         &lt;system.web&gt;
      &lt;pages&gt;
          &lt;controls&gt;
              &lt;add tagPrefix="ajax" namespace="AjaxControlToolkit" assembly="AjaxControlToolkit"/&gt;
              &lt;add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/&gt;
              &lt;add tagPrefix="asp" namespace="System.Web.UI.WebControls" assembly="System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/&gt;
          &lt;/controls&gt;
      &lt;/pages&gt;
      &lt;compilation debug="true" targetFramework="4.0"&gt;
          &lt;assemblies&gt;
              &lt;add assembly="System.Web.Extensions.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/&gt;
              &lt;add assembly="System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/&gt;
              &lt;add assembly="System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/&gt;&lt;/assemblies&gt;&lt;/compilation&gt;
    &lt;/system.web&gt;
      &lt;/configuration&gt;
  </code></pre>
  
  <p>The aspx page looks like this:</p>
  
  <pre><code>     &lt;form id="form1" runat="server"&gt;
         &lt;div&gt;
          &lt;asp:ScriptManager ID="sm" runat="server"&gt;&lt;/asp:ScriptManager&gt;
          &lt;ajax:ComboBox runat="server" AutoCompleteMode="SuggestAppend"&gt;
            &lt;asp:ListItem&gt;ddd&lt;/asp:ListItem&gt;
            &lt;asp:ListItem&gt;fff&lt;/asp:ListItem&gt;
            &lt;asp:ListItem&gt;gggg&lt;/asp:ListItem&gt;
            &lt;asp:ListItem&gt;hhhhh&lt;/asp:ListItem&gt;
          &lt;/ajax:ComboBox&gt;    
         &lt;/div&gt;
      &lt;/form&gt;
  </code></pre>
  
  <p>I have even tried deleting the schema files from C:\Documents and Settings\xxx\Application Data\Microsoft\VisualStudio\10.0\ReflectedSchemas location.</p>
  
  <p>Please help me in successfully implementing the Combobox control.
  Thanks!</p>
  
  <p><strong>Edited:</strong></p>
  
  <p>As a different approach, I created a new website and installed the latest version of AjaxControlToolkit using <strong>NuGet</strong>. I rebuilt the solution. I still could not see the Ajax controls in intellisense.
  Is there anything else that needs to be done to implement it? Please help!!</p>