How to disable the menu?

Brad:

I would not think so, I built a demo project to look at the problem and I had a main MDI form with tabs and it did not present any problems.  Did you try building a clean project to see if you could get some of other things to work (like the controlbox property?). 

Yeah, it does not make the close X go away, it is just intercepting and blocking the command to close the form.  The problem is interesting because I don't understand why setting the form's control box property is not hiding the controls.  What OS and version of VS are you using?  I can look at it in Vista or XP with 2003 or 2005.  Just for grins, fire up a new win forms C# project, make the default form an MDI parent, set the control box property to false on that form and run it and tell me if you see the control box.  I did the same on an XP box with VS 2005; when I run it, I don't see the control box at all.

Outside of using a borderless form (which surely won't show a control box) I believe there is a way in the API that you can block the display of the close X; I will look into that.

Opps, maybe you want to minimize and maximize but just want to disable the Close 'X' button; if so, this bit of code will disable the close 'X' button if you drop it into the form's code:  (it also disables Alt-F4 so you will have to provide some other method for exiting the application)

protected override void WndProc(ref System.Windows.Forms.Message m)
{
     if (m.Msg != 0x0010)
     {
          base.WndProc(ref m);
     }
     else
     {
          //do nothing
     }
}