Textbox NumericUpDownExtender RangeValidator js error

Using toolkit version 3.5.60919

I have the following controls on a content page..

<asp:ImageButton ID="QtyUp" runat="server"
                 AlternateText='<%$ Resources:Resource, QtyUp %>'
                 ToolTip='<%$ Resources:Resource, QtyUp %>' /><asp:TextBox ID="ItemQty" runat="server" style="text-align: center;"
             Text="1" Width="15" /><asp:ImageButton ID="QtyDown" runat="server"
                 AlternateText="<%$ Resources:Resource, QtyDown %>"
                 ToolTip='<%$ Resources:Resource, QtyDown %>' /><asp:RangeValidator ID="ItemQtyRangeValidator" runat="server" SetFocusOnError="true"
                    ControlToValidate="ItemQty" Type="Integer" Display="Dynamic"
                    MinimumValue="1" MaximumValue="20"
                    ErrorMessage="<%$ Resources:Resource, QtyInvalid %>" /><ajax:NumericUpDownExtender ID="ItemQtyUpDown" runat="server"
                            TargetControlID="ItemQty"
                            Minimum="1" Maximum="20"
                            TargetButtonDownID="QtyDown"
                            TargetButtonUpID="QtyUp" /><ajax:RoundedCornersExtender ID="RCEqty" runat="server"
                             TargetControlID="ItemQty" BorderColor="Black"
                             Radius="4" Corners="All" />

When I run this, I get an error..

Microsoft JScript runtime error: Unable to get value of the property 'srcElement': object is null or undefined

It highlights some code in the framework..

function ValidatorOnChange(event) {
    if (!event) {
        event = window.event;
    }
    Page_InvalidControlToBeFocused = null;
    var targetedControl; if ((typeof(event.srcElement) != "undefined") && (event.srcElement != null)) {         targetedControl = event.srcElement;
    }
    else {
        targetedControl = event.target;
    }

IF I remove the NumericUpDownExternder, it works fine..

Any ideas?