■ More than one condition can cause this error:
 
  • You tried to add non-menu controls to an MDI form.
 
  • You tried to set the FormType property of a form to
    1 - MDI when it contains non-menu controls.
 
■ Possible solutions:
 
  • To add non-menu controls to an MDI form, you must first
    change the form's FormType property to 0 - Normal.
 
  • To make a form containing non-menu controls an MDI form,
    you must first delete all controls except menus and then
    set the FormType property to 1 - MDI.
 
■ If you need additional help, move the cursor to a keyword
  and press F1 to open the Help window.