Simple reproducible is attached to illustrate the problem.

A workaround may be replacing RadButtons that invokes such postbacks with regular buttons and using a form decorator

Alternatively, you can simply disable the handler URL encryption

You can also put the following in the global.asax file to prevent the version from rendering on the page markup
        protected void Application_BeginRequest(object sender, EventArgs e)
        {
			System.Web.HttpContext.Current.Items["_!TelerikVersionStampRendered"] = true;
        }
or you can add the same line in a global Page_Load handler (e.g., in a base page class or in the master page your project uses)