Could be it, or the CellCickActionDefault="RowSelect"...most probably you will need to switch features off one by one in ordetr to see which specific one (or combination of which) does this

In any case, calling s

igtbl_needPostBack(gridName);

the client-side event handler should probably resolve the problem.

This is what the control def looks like, is it the Band AllowUpdate?

<igtbl:UltraWebGrid ID="UltraWebGridActivities" runat="server" Height="370px" Style="top: 0px"
                            Width="99%" StyleSetName="EpitomeBlue" StyleSetPath="../ig_res">
                            <Bands>
                                <igtbl:UltraGridBand AllowUpdate="Yes">
                                    <AddNewRow View="NotSet" Visible="NotSet">
                                    </AddNewRow>
                                </igtbl:UltraGridBand>
                            </Bands>
                            <DisplayLayout AllowColSizingDefault="Free" AllowColumnMovingDefault="OnServer" AllowSortingDefault="Yes"
                                BorderCollapseDefault="Separate" HeaderClickActionDefault="SortMulti" Name="UltraWebGridActivities"
                                RowHeightDefault="20px" Version="4.00" ViewType="Hierarchical" StationaryMargins="Header"
                                TableLayout="Fixed" CellClickActionDefault="RowSelect" SelectTypeRowDefault="Extended" AllowUpdateDefault="Yes">
                                <ActivationObject BorderColor="" BorderWidth="">
                                </ActivationObject>
                                <FrameStyle Width="99%" Height="370px" TextOverflow="Ellipsis">
                                </FrameStyle>
                                <Pager AllowPaging="True" AllowCustomPaging="True" StyleMode="ComboBox" PagerAppearance="Both"
                                    PageSize="20">
                                </Pager>
                                <ClientSideEvents CellClickHandler="UltraWebGridActivities_CellClickHandler" InitializeLayoutHandler="defaultController.initGrid" />
                            </DisplayLayout>
                        </igtbl:UltraWebGrid>

 Most probably this is a setting (e.g. a property set to a value that requires postback). Maybe you have hooked some server-side events, or enabled server-side editing / updating in any way? I started with a very basic grid and hooked only the client-side CellClickHandler and the grid did not postback for me when clicking on a cell (I verified that with FireBug for FireFox, which works pretty much in a similar way like IE Web Dev Toolbar and Fiddler)

    <igtbl:UltraWebGrid ID="UltraWebGrid1" runat="server" Height="200px"
        Width="325px">           
        <Bands>
            <igtbl:UltraGridBand>
                <AddNewRow View="NotSet" Visible="NotSet">
                </AddNewRow>               
            </igtbl:UltraGridBand>
        </Bands>
        <DisplayLayout BorderCollapseDefault="Separate" Name="UltraWebGrid1"
            RowHeightDefault="20px" Version="4.00" ViewType="Hierarchical">
            <ClientSideEvents CellClickHandler="CellClick" />
        </DisplayLayout>       
    </igtbl:UltraWebGrid>
   
    <script type="text/javascript" >
   
    function CellClick(gridID, cellID)
    {
        alert(cellID);
    }
   
    </script>

What could be different in your case? 

 Hi Rumen and thanks for your reply. The setValue() and other methods now work as expected; the problem was really with the postback-ing of the grid on a client click. Any changes I had made to the DOM, wether via setValue() or otherwise were getting immediately overwritten by the postback return content. I only found this after running fiddler and seeing the traffic to the server after the client click. 

Do you know why the grid will post back if a client event handler is registered for the event? It does not make sense to me that a call to the server is necessary in those cases. 

Thanks,

Andrew