S error is thrown when the Rotator items do not fill its viewport and EnableRandomOrder="true". The problem occurs in all render modes, when the width of the Rotator is set to 100%.

Error message:
Uncaught Error: Sys.ArgumentNullException: Value cannot be null.
Parameter name: element

WORKAROUNDS:
- set EnableRandomOrder="false" or
- set fixed width to the control, e.g. Width="1000px"



Reproduction code:
        <telerik:RadRotator ID="ProductRotator" runat="server" RotatorType="AutomaticAdvance" Height="100"
            ItemHeight="90" Skin="Default" Width="100%" EnableRandomOrder="true" ScrollDuration="1000">
            <ItemTemplate>
                <div style="width:100px; height: 75px; border: 1px solid red">
                    <%# Eval("title")%>
                </div>
            </ItemTemplate>
        </telerik:RadRotator>


    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            ProductRotator.DataSource = GetData();//Producten;
            ProductRotator.DataBind();
        }
    }
    private object GetData()
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("title", typeof(string));
        dt.Columns.Add("desc", typeof(string));
        dt.Rows.Add("T1", "AAA");
        dt.Rows.Add("T2", "BBB");
        dt.Rows.Add("T3", "CCC");
        return dt;
    }

When you wrap an image in an anchor element in the content of an ItemTemplate of RadRotator, the image will not be clickable.

The items of RadRotator are not rotated correctly when the FrameDuration property is set to a small value and the PauseOnMouseOver property is set to true.

There are problems with the position of the control buttons of RadRotator in IE and Opera when lightweight render mode of the control is enabled either by setting RenderMode to Lightweight or by setting RenderMode to Auto, which in turn enables lightweight mode in the appropriate browsers.

The workaround for this issue is to set the RenderMode property to Classic.

When the RadRotator control loads its items from a web service, it performs two requests and then stops.

When RadRotator is configured to load its items from a web service (http://demos.telerik.com/aspnet-ajax/rotator/examples/loadondemand/defaultcs.aspx) and it is using the MetroTouch skin, the loading image that is displayed until the items are populated, is missing.

You can observe it here: http://demos.telerik.com/aspnet-ajax/rotator/examples/carouselmode/defaultcs.aspx by clicking either of the sequences. Note: set the rotator to CarouselButtons to avoid cinfusion stemming from automatic advance.
- red, grey, green. You will see red instead of green
- blue, green, gray. You will see blue instead of gray
One more item was rotated in each case.

A workaround is to disable animations for these second and last items when their counterpart is currently shown:
function OnClientItemClicked(sender, args) {
	var shouldAnimate = true;
	var indextToChangeTo = args.get_item().get_index();
	var currIndex = sender.get_currentItemIndex();
	var itemsCount = sender.get_items().length;
	if (currIndex == itemsCount - 1 && indextToChangeTo == 1 || //last item is shown, the second item is clicked
		currIndex == 1 && indextToChangeTo == itemsCount - 1) { //second item is shown, last item is clicked
		shouldAnimate = false;
	}
	sender.set_currentItemIndex(indextToChangeTo, shouldAnimate);
}

There are multiple scenarios where the Ticker control does not behave consistently with & values.

Text content that is not consistent:

text & -> text &

The client-side events ClientMouseOver and ClientMouseOut are not fired when the items in the rotator are hovered.

When the rotator items are added declaratively by placing RadRotatorItem element in the Items collection, changing ItemWidth on the code-behind does not affect the width of the items.

When 'FrameDuration' is set with small value, for example 1, the rotator will not be paused on mouse over even if 'PauseOnMouseOver' is set to 'true'.

If a RadRotator is set in AutomaticAdvance mode and its property PauseOnMouseOver is set to true, it will start scrolling incorrectly when the cursor is moved over the items in the scroll direction before the scrolling is completed.

Currently the RadRotator is not displayed under mobile Chrome for iOS.

The issue could be worked around by switching Chrome to "request desktop site" mode from the browser menu.
 

When a RadRotator is configured in CoverFlowButtons mode and the currently displayed item is set via the client-side method set_currentItemIndex before the items are scrolled manually, the enabled/disabled state will not be applied correctly to the control buttons.