Tico Breezy, tenta assim:
'No módulo
Option Explicit
Private Declare Function GetWindowLong Lib "user32" _
Alias "GetWindowLongA" (ByVal hWnd As Long, _
ByVal nIndex As Long) As Long
Private Declare Function SetWindowLong Lib "user32" _
Alias "SetWindowLongA" (ByVal hWnd As Long, _
ByVal nIndex As Long, ByVal dwNewLong As Long) _
As Long
Private Const GWL_STYLE = (-16)
Private Const WS_MINIMIZEBOX = &H20000
Private Const WS_MAXIMIZEBOX = &H10000
Public Sub NoMaxBox(f As MDIForm)
Dim l As Long
l = GetWindowLong(f.hWnd, GWL_STYLE)
l = l And Not (WS_MAXIMIZEBOX)
l = SetWindowLong(f.hWnd, GWL_STYLE, l)
End Sub
Public Sub NoMinBox(f As MDIForm)
Dim l As Long
l = GetWindowLong(f.hWnd, GWL_STYLE)
l = l And Not (WS_MINIMIZEBOX)
l = SetWindowLong(f.hWnd, GWL_STYLE, l)
End Sub
'No form
Private Sub MDIForm_Load()
Call NoMinBox(MDIForm1)
Call NoMaxBox(MDIForm1)
End Sub