I add my custom menus with the following code (it adds a submenu with some menuitems under the dimension menu).
[code]
AcadApplication app = (AcadApplication)Autodesk.AutoCAD.ApplicationServices.Application.AcadApplication;
AcadMenuBar menuBar = app.MenuBar;
AcadPopupMenu dimensionMenu = null;
//Find the dimension menu
for (int i = 0; i < menuBar.Count; i++)
if (menuBar.Item(i).TagString.Equals("ID_MnDimensi"))
dimensionMenu = menuBar.Item(i);
if (dimensionMenu != null)
{
dimensionMenu.AddSeparator(dimensionMenu.Count);
AcadPopupMenu camSubMenu = dimensionMenu.AddSubMenu(dimensionMenu.Count, "CAM Dimensions");
camSubMenu.AddMenuItem(dimensionMenu.Count, "Square", "SQUAREDIM ");
camSubMenu.AddMenuItem(dimensionMenu.Count, "Sphere Radius", "SPHERERADIUS ");
camSubMenu.AddMenuItem(dimensionMenu.Count, "Sphere Diameter", "SPHEREDIAMETER ");
camSubMenu.AddMenuItem(dimensionMenu.Count, "Key", "KEYDIM ");
camSubMenu.AddMenuItem(dimensionMenu.Count, "Leader", "LEADERDIM ");
}
[/code]
As you can see I don't use a cui file, but the menu appears instantly.
Hope I could help you.