Download the version of RadControls for ASP.NET AJAX you have under your Telerik account and add a reference to it inside your DNN project (either in the /bin folder or Global Assembly Cache). In case you have <bindingRedirect> element inside DNN’s web config file, modify it to match the assembly version number of Telerik.Web.UI.dll and Telerik.Web.Design.dll, for example:
NET 3.5:
<dependentAssembly>
<assemblyIdentity name="Telerik.Web.UI" publicKeyToken="121fae78165ba3d4"/>
<bindingRedirect oldVersion="2008.0.0.0-2020.0.0.0" newVersion="2009.2.701.35"/>
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Telerik.Web.Design " publicKeyToken="121fae78165ba3d4"/>
<bindingRedirect oldVersion="2008.0.0.0-2020.0.0.0" newVersion="2009.2.701.35"/>
</dependentAssembly>
NET 2:
<dependentAssembly>
<assemblyIdentity name="Telerik.Web.UI" publicKeyToken="121fae78165ba3d4"/>
<bindingRedirect oldVersion="2008.0.0.0-2020.0.0.0" newVersion="2009.2.701.20"/>
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Telerik.Web.Design " publicKeyToken="121fae78165ba3d4"/>
<bindingRedirect oldVersion="2008.0.0.0-2020.0.0.0" newVersion="2009.2.701.20"/>
</dependentAssembly>