After this update, the page is showing this error: The base class includes the field 'RadAjaxManager1', but its type (Telerik.Web.UI.RadAjaxManager) is not compatible with the type of control (Telerik.Web.UI.RadAjaxManager).
I searched on google for a little while, and based on this ASP.Net post it looks like there is some problem in the web.config file. Maybe try checking in Compilation >> Assemblies that everything there is updated to the latest and greatest?