RadAjax and Standard Validators RadAjax controls fully support server and client-side validation with the Standard Validators. However when the page uses ValidationSummary control with CustomValidator which performs server-side validation, you need to wrap it in an ASP:Panel and add the panel to the UpdatedControls collection in the ajax settings when the page is ajaxfied with RadAjaxManager, or add the ValidationSummary control in the RadAjaxPanel control if such is used for the page ajaxification.

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<telerik:RadAjaxManager ID="RadAjaxManager1" runat="server">
    <AjaxSettings>
        <telerik:AjaxSetting AjaxControlID="btnValidate">
            <UpdatedControls>
                <telerik:AjaxUpdatedControl ControlID="TextBox1" />
                <telerik:AjaxUpdatedControl ControlID="pnlValidationSummary" />
            </UpdatedControls>
        </telerik:AjaxSetting>
    </AjaxSettings>
</telerik:RadAjaxManager>
<asp:TextBox ID="TextBox1" runat="server" />
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="TextBox1"
    Display="None" ErrorMessage="Required Field" />
<asp:Button ID="btnValidate" runat="server" />
<asp:Panel ID="pnlValidatorSummary" runat="server">
    <asp:ValidationSummary ID="ValidationSummary1" runat="server" />
</asp:Panel>

RadAjaxTimer control We decided not to include a Timer control in RadAjax for ASP.NET AJAX. This is due to the fact that the timer control is a postback control and does not include ajax capabilities by itself. The second reason is that a timer control is already included in MS AJAX that offers the basic functionality we did. Here is an online demo which illustrates sample approach.

Ajaxified control postbacks when having no updated controls For example the following RadAjaxManager setting will not ajaxify the button:

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<telerik:RadAjaxManager ID="RadAjaxManager1" runat="server">
    <AjaxSettings>
        <telerik:AjaxSetting AjaxControlID="Button1">                
        </telerik:AjaxSetting>
    </AjaxSettings>
</telerik:RadAjaxManager>

You can work around that by adding a control to be updated. For example - the same AJAX initiator control:

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<UpdatedControls>
    <telerik:AjaxUpdatedControl ControlID="Button1" />
</UpdatedControls>

RadAjaxManager and RadAjaxPanel at the same application There are some known issues when using both the manager and the panel in some complex applications - MasterPage or WebUserControls. However, note that a single RadAjaxManager (and no panels) in the master/main page could handle all the scenarios.

Client-Side events OnRequestSent and OnResponseReceived missing Those events are removed in RadAjax for ASP.NET AJAX. There is no way to "simulate" them due to the way ASP.NET AJAX works. Please use OnRequestStart and OnResponseEnd for your needs.

Various controls not supported by the MS AJAX framework See a full list of controls, not compatible with RadAjax for ASP.NET AJAX here.

Ajax requests may not work in all scenarios when setting the RestoreOriginalRenderDelegate property to false or inheriting from RadAjaxPage (to support medium trust in DNN/Sharepoint) Please be aware of this fact when configuring RadAjaxManager or RadAjaxPanel for your particular project schema.