When attempting to run an application that uses certain Telerik controls, you may run into the error below:

 System.InvalidOperationException: ‘~/Telerik.Web.UI.WebResource.axd’ is missing in web.config. RadStyleSheetManager requires a HttpHandler registration in web.config. Please, use the control Smart Tag to add the handler automatically, or see the help for more information: Controls > RadStyleSheetManager at Telerik.Web.UI.RadStyleSheetManager.OnPreRender(EventArgs e) at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

I’ve seen that error on new DotNetNuke installations but it certainly isn’t specific to DNN, nor is it a problem with the Telerik controls. The issue is that the Integrated Pipeline Mode and Classic Modes handle the registration slightly differently within the web.config file

To resolve this error you can make changes to your web.config file, or, a perhaps faster and easier solution, is to change your site’s ASP.NET version to Classic Mode – both seem to work equally well.

Happy Hosting!