What we are looking to achieve is easiest to show with screenshots from our app that uses Infragistics' old UltraWebMenu and UltraWebGrid controls.  In these screenshots, I've obfuscated our data with black and red marks for confidentiality.  Each screenshot shows the same grid but with a different context menu appearing over it.  The red mark indicates which cell was clicked to make the context menu appear.  Notice that the contents of the context menu differ depending on which row was clicked (the contents of the menu are dependent on the data in the row and some server-side logic).

Now we are trying to replicate the above using WebDataMenu and WebDataGrid.  Per your reply, I put the following in my markup inside the <Columns> element of a WebDataGrid:

<iggrid:TemplateDataField Key="MenuAction" Width="10%">

    <Header Text="Ref Number"></Header>

    <ItemTemplate>

    <asp:Label ID="lblLaunchMenu" runat="server" Text="Launch Menu" Font-Underline="true" ForeColor="Blue" CssClass="Label" Visible="false" />

        <igmenu:WebDataMenu ID="mnuActionMenu" runat="server" IsContextMenu="true">

            <Items>

                <igmenu:DataMenuItem>

                    <Template>

                        <p>Dummy Menu Item</p>

                    </Template>

                </igmenu:DataMenuItem>

            </Items>

        </igmenu:WebDataMenu>

     </ItemTemplate>

</iggrid:TemplateDataField>

In the code behind, in the handler for the grid's InitializeRow event, I have the following:

WebDataMenu actionMenu = row.Items.FindItemByKey(COL_ACTION).FindControl("mnuActionMenu") as WebDataMenu;

actionMenu.ID = "menuForAccount" + accountNumber // give each grid row's menu a unique ID, account number is different in each grid row

//this is pseudocode for loop that adds menu items to each menu, the important point here is that "i" makes each menu item unique within a given menu

int i = 0;

loop

    actionMenu.Items.Add(new DataMenuItem { Enabled = true, Visible = true, Text = "foo" + i, NavigateUrl = "/bar/" + i }

    i++;

end loop

var fullMenuName = ClientID.Replace("_", "") + actionMenu.ID;

lblLaunchMenu.Attributes.Add("onmouseup", "BLOCKED SCRIPTif(event.button == 0 || event.button == 1){igmenu_showMenu('" + fullMenuName + "', event);event.returnValue = false;event.cancelBubble=true;}");

We copied the last two line above from our app that uses the old Infragistics controls, but when igmenu_showMenu executes, it can't find an element whose id is fullMenuName, so it pops up this message (I've debugged into igmenu_showMenu and saw where this happens):

So that's where we are at this point.  Any help would be appreciated.