I have had the following code which was not working. When i replaced RadAjaxManagerProxy with RadAjaxManager, the code worked fine.
<telerik:RadCalendar ID="RadRadCalendar1" AutoPostBack="true" runat="server" Skin="Web20" ></telerik:RadCalendar>
<asp:Content runat=server ContentPlaceHolderID=Main>
<telerik:RadAjaxManagerProxy id="RadAjaxManager1" runat="server">
<AjaxSettings>
<telerik:AjaxSetting AjaxControlID="RadRadCalendar1">
<UpdatedControls>
<telerik:AjaxUpdatedControl LoadingPanelID="Loadingpanel" ControlID="RadRadCalendar1"></telerik:AjaxUpdatedControl>
</UpdatedControls>
</telerik:AjaxSetting>
</AjaxSettings>
</telerik:RadAjaxManagerProxy>
<asp:Content runat=server ContentPlaceHolderID=Main>
<telerik:RadAjaxManagerProxy id="RadAjaxManager1" runat="server">
<AjaxSettings>
<telerik:AjaxSetting AjaxControlID="RadDatePicker1">
<UpdatedControls>
<telerik:AjaxUpdatedControl LoadingPanelID="Loadingpanel" ControlID="RadDatePicker1"></telerik:AjaxUpdatedControl>
</UpdatedControls>
</telerik:AjaxSetting>
<telerik:AjaxSetting AjaxControlID="rcStartDate">
<UpdatedControls>
<telerik:AjaxUpdatedControl ControlID="rcStartDate"></telerik:AjaxUpdatedControl>
</UpdatedControls>
</telerik:AjaxSetting>
</AjaxSettings>
</telerik:RadAjaxManagerProxy>
RadAjaxManagerProxy