Public Declare Function GetSystemMenu Lib "user32" _
	(ByVal hWnd As Long, ByVal bRevert As Long) As Long
Public Declare Function ModifyMenu Lib "user32" Alias "ModifyMenuA" _
	(ByVal hMenu As Long, ByVal nPosition As Long, _
	ByVal wFlags As Long, ByVal wIDNewItem As Long, _
	ByVal lpString As Any) As Long
Public Declare Function DrawMenuBar Lib "user32" _
	(ByVal hWnd As Long) As Long
'
Global Const MF_BYCOMMAND = &H0&
Global Const MF_ENABLED = &H0&
Global Const MF_GRAYED = &H1&
'
Public Const SC_CLOSE = &HF060&
' Básicamente lo que se hace es dibujar una caba sobre el botón actual
'la cual lo bloquea

Private Sub Bloquear_Cerrar()
Dim hMenu As Long
	'
hMenu = GetSystemMenu(hWnd, 0)
	' Deshabilitar el menú cerrar del formulario
Call ModifyMenu(hMenu, SC_CLOSE, MF_BYCOMMAND Or MF_GRAYED, -10, "Close")
End Sub
Private Sub Form_Load()
Bloquear_Cerrar ' llamamos a nuestro evento
End Sub