<asp:ScriptManager ID="ScriptManager1" runat="server" />
     <asp:UpdatePanel ID="UpdatePanel1" runat="server" ChildrenAsTriggers ="false">
     <ContentTemplate>
             <asp:GridView ID="gvEventMechanic" runat="server" AutoGenerateColumns="False" PageSize="5"
                        GridLines="None" AllowSorting="true" BorderWidth="1"
                        EnableViewState="true" AllowPaging="true">
            <Columns>
                <asp:TemplateField>
                    <HeaderTemplate>
                        Disable
                        </HeaderTemplate>
                    <ItemStyle HorizontalAlign="Center" />
                    <ItemTemplate>
                        <asp:CheckBox ID="chkDelete" runat="server" AutoPostBack="true" ></asp:CheckBox>
                    </ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>
        </ContentTemplate>
         <Triggers>
                <asp:AsyncPostBackTrigger ControlID="chkDelete" EventName="CheckBoxEventChanged" />
            </Triggers>
        </asp:UpdatePanel>

$('#input[type=checkbox][id*=chkDelete]').change(function(){
        $('#button').toggleClass('disabled');
   });

$('#input[type=checkbox][id*=chkDelete]').change(function(){
        if ($(this).is(':checked'))
        {
            $('#button').removeAttr('disabled');
        }
        else
        {
            $('#button').attr('disabled', 'disabled');
        }
   });

// If you bind a list of objects as your data source you can use this to get the
// index into the list.
protected void OnCheckedChanged( Object sender, EventArgs e )
{
    if ( sender is CheckBox )
    {
        // we do this to get the index into the list of the item we want to work with.
        CheckBox     cb = sender as CheckBox;
        GridViewRow gvr = cb.NamingContainer as GridViewRow;

        int dataItemIndex = gvr.DataItemIndex;  // index into your list, regardless of page
        int rowIndex      = gvr.RowIndex;       // row index in gridview.
    }
}