The UltraTextEditor is positioning a .NET TextBox within its bounds, even when it is set to ReadOnly mode.  What you could do is hook the DoubleClick event of the TextBox in the ControlAdded event of the editor, i.e.:

private void ultraTextEditor1_ControlAdded(object sender, ControlEventArgs e)
{
    e.Control.DoubleClick += new EventHandler(Control_DoubleClick);
}

private void ultraTextEditor1_ControlRemoved(object sender, ControlEventArgs e)
{
    e.Control.DoubleClick -= new EventHandler(Control_DoubleClick);
}

void Control_DoubleClick(object sender, EventArgs e)
{
    this.ultraTextEditor1.ReadOnly = false;
}

-Matt

 FAQ:Mouse events such as MouseDown, MouseUp, and DoubleClick do not fire for an UltraWinEditor it is in edit mode.

In this case, you need to handle the events of the grid, since the UltraTextEditor is not being used as a control anymore, but rather is providing the editor that the grid positions in its cell.  This KB article should help you determine which cell was clicked in the grid.  If you're referring to the same problem in the previous posts, then you would do the same workaround that was given, except that you'd be hooking the ControlAdded/Removed of the grid instead of the UltraTextEditor.

-Matt