Wondering why your page is not getting postback when you select any dropdown item even-though you have set AutoPostback property to true? If so, then it can be fixed by adding below configuration in your web.config file under <typesThatShouldNotBeExpanded> section.
System.Web.UI.WebControls.Repeater System.Web.UI.WebControls.DataList System.Web.UI.WebControls.GridView System.Web.UI.WebControls.ListView System.Web.UI.WebControls.FormView Microsoft.Reporting.WebForms.ReportViewer Telerik.Web.UI.RadGrid System.Web.UI.WebControls.LoginView System.Web.UI.WebControls.DropDownList
