Solved: “Unknown server tag telerik:RadScriptManager”

If you are using third-party .NET component libraries such as Telerik or DevExpress, you may come across the error message below while trying to include controls in your page.

Server Error in ‘/TestASPNET’ Application.

Parser Error
Description: An error occurred during the parsing of a resource required to service this request. Please review the following specific parse error details and modify your source file appropriately.

Parser Error Message: Unknown server tag ‘telerik:RadScriptManager’.

Solution

Make sure to include 2 DLL files below in your project references of Visual Studio:

  • Telerik.Web.UI
  • Telerik.Web.UI.Skins

If you are still receiving the error above, add a reference to your Telerik assembly in your web.config file. You can use the following lines to make this reference.

<system.web>
  <pages viewStateEncryptionMode="Always" controlRenderingCompatibilityVersion="3.5" clientIDMode="AutoID">
    <controls>
      <add tagPrefix="telerik" namespace="Telerik.Web.UI" assembly="Telerik.Web.UI"/>
    </controls>
  </pages>
</system.web>