Solved: “Unrecognized tag prefix or device filter ‘telerik'”

I came across “unrecognized tag prefix” error while trying to use Telerik’s ASP.NET AJAX controls. Here is how the error message looks like:

Warning – Unrecognized tag prefix or device filter ‘telerik’

Solution

  1. Make sure to add Telerik DLLs into the bin folder of your project
  2. Add the following handlers into your web.config file (in section):

    <pages>
          <controls>
            <add tagPrefix="telerik" namespace="Telerik.Web.UI" assembly="Telerik.Web.UI"/>
          </controls>
    </pages>
    <httpHandlers>
          <add path="ChartImage.axd" type="Telerik.Web.UI.ChartHttpHandler" verb="*" validate="false"/>
          <add path="Telerik.Web.UI.SpellCheckHandler.axd" type="Telerik.Web.UI.SpellCheckHandler" verb="*" validate="false"/>
          <add path="Telerik.Web.UI.DialogHandler.aspx" type="Telerik.Web.UI.DialogHandler" verb="*" validate="false"/>
          <add path="Telerik.RadUploadProgressHandler.ashx" type="Telerik.Web.UI.RadUploadProgressHandler" verb="*" validate="false"/>
          <add path="Telerik.Web.UI.WebResource.axd" type="Telerik.Web.UI.WebResource" verb="*" validate="false"/>
    </httpHandlers>

Similar solutions apply to the same type of message for other components.