Hi! I have a page with an update panel. I'm not using your callback panel because I also have a custom control that doesn't work inside your panel.
My problem is that my Grid using a CustomColumn with a select box, doesn't fire the 
ClientSideEndEdit & ClientSideBeginEdit javascript event when I edit my cell. If I remove the update panel of the page, it's working. Do you know why it can't fired Javascript event?
This part of the code is in a CustomServerControl inserted in an aspx page. The update panel is in the aspx page for the whole application.
    
        Code: HTML/ASPX
        
        <script type="text/javascript">
    var g_curItemIndex = -1;
    function beginEdit(cell) {
        g_curItemIndex = cell.getItemIndex();
        var v = cell.getValue();
        var dropDownBox = document.getElementById("seanceTypeList");
        for (var i = 0; i < dropDownBox.options.length; i++) {
            if (dropDownBox.options[i].value == v) {
                dropDownBox.selectedIndex = i;
                return;
            }
        }
        dropDownBox.selectedIndex = 0;
    }
    function endEdit(cell) {
        var dropDownBox = document.getElementById("seanceTypeList");
        var selectedIndex = dropDownBox.selectedIndex;
        if (selectedIndex > 0) {
            return dropDownBox.options[selectedIndex].value;
        }
        return null;
    }
    
</script>
<eo:Grid ID="seanceGrid" KeyField="SeanceID" runat="server" GridLines="Both" GridLineColor="0, 51, 0"
                    ForeColor="#003300" Font-Names="Verdana" BorderStyle="Solid" BorderWidth="1px"
                    Font-Size="8.75pt" FullRowMode="False" Font-Bold="False" Font-Italic="False"
                    Font-Overline="False" Font-Strikeout="False" Font-Underline="False" Height="500px"
                    ItemHeight="50" Width="680px" AllowNewItem="True" AllowPaging="True">
                    <ColumnHeaderStyle CssText="text-align: left; padding-top: 3px; color: #003300; font-weight: bold; background: #ffffff url('./Images/GridHeader-Bg.png') repeat-x;">
                    </ColumnHeaderStyle>
                    <Columns>
                        <eo:CustomColumn HeaderText="Type" Width="100" DataField="Description" ClientSideEndEdit="endEdit"
                            ClientSideBeginEdit="beginEdit">
                            <CellStyle CssText="text-align: left; padding-top: 2px; padding-right: 2px;" />
                            <EditorTemplate>
                                <select id="seanceTypeList" style="width: 100px">
                                    <option>Choisir</option>
                                    <asp:Repeater runat="server" ID="seanceTypeRepeater">
                                        <ItemTemplate>
                                            <option value='<%#DataBinder.Eval(Container.DataItem, "Description")%>'>
                                                <%#DataBinder.Eval(Container.DataItem, "Description")%>
                                            </option>
                                        </ItemTemplate>
                                    </asp:Repeater>
                                </select>
                            </EditorTemplate>
                        </eo:CustomColumn>
                    </Columns>
                </eo:Grid>