enable disable dropdownlist with respect to checkbox

I have one dropdownlist and a checkbox in RadGrid.

I have set dropdown Enabled="false" initially. So on page load, dropdownlist will be disabled, now if I check any checkbox from RadGrid, dropdown should be enabled.

Checkbox:

<telerik:GridTemplateColumn UniqueName="CheckBoxTemplateColumn">
                                                                <ItemTemplate>
                                                                    <asp:CheckBox ID="CheckBox1" runat="server" OnCheckedChanged="ToggleRowSelection"
                                                                        AutoPostBack="True" />
                                                                </ItemTemplate>
                                                                <HeaderTemplate>
                                                                    <asp:CheckBox ID="headerChkbox" runat="server" OnCheckedChanged="ToggleSelectedState"
                                                                        AutoPostBack="True" />
                                                                </HeaderTemplate>
                                                            </telerik:GridTemplateColumn>

Dropdownlist:

<telerik:RadDropDownList ID="ddlAction" Enabled="false" DefaultMessage="Action" AutoPostBack="true" DataValueField="action" OnSelectedIndexChanged="ddlAction_SelectedIndexChanged"  runat="server">
                                                           <Items>
                                                               <telerik:DropDownListItem Text="" Value="" />
                                                               <telerik:DropDownListItem Text="Refresh Mail Status" Value="Refresh Mail Status" />
                                                               <telerik:DropDownListItem Text="Send All" Value="Send All" />
                                                               <telerik:DropDownListItem Text="Send Selected" Value="Send Selected"/>
                                                               <telerik:DropDownListItem Text="Remove" Value="Remove" />
                                                           </Items>

                                                        </telerik:RadDropDownList>

Code behind:

protected void ddlAction_SelectedIndexChanged(object sender, DropDownListEventArgs e)
        {
            CheckBox chk = (CheckBox)sender;
            chk.FindControl("CheckBox1");

            if (!chk.Checked) { ddlAction.Enabled = true; }

}