ajax manager problem

[Selami]

hello team...
I m new telerik control...
my code doesnt work-->
  <telerik:RadAjaxManager ID="RadAjaxManager1" runat="server"  >
                            <AjaxSettings>
                                <telerik:AjaxSetting AjaxControlID="checkEngelliyim">
                                    <UpdatedControls>
                                        <telerik:AjaxUpdatedControl ControlID="comboEngelli" />
                                        <telerik:AjaxUpdatedControl ControlID="comboYuzde" />
                                        <telerik:AjaxUpdatedControl ControlID="txtEngelliAciklama" />
                                    </UpdatedControls>
                                </telerik:AjaxSetting>
                            </AjaxSettings>
                        </telerik:RadAjaxManager>

    <td width="5%" style="padding-bottom:5px">
                                    <asp:CheckBox ID="checkEngelliyim" Text="" runat="server" AutoPostBack="True"
                                        oncheckedchanged="checkEngelliyim_CheckedChanged" />
                                </td>
(aspx)
     protected void checkEngelliyim_CheckedChanged(object sender, EventArgs e)
        {
            txtEngelliAciklama.Enabled = checkEngelliyim.Checked;
            comboEngelli.Enabled = checkEngelliyim.Checked;
            comboYuzde.Enabled = checkEngelliyim.Checked;
        }
(cs code)

checkEngelliyim is checkbox and auto postback true

I m getting java script error in i.e  explorer mozilla doesnt fire error...
and same code is working another page....I couldnt understand this....I m very bored