Option Compare Database
Private Declare Function GetSystemMenu Lib "user32" (ByVal hWnd As Long, _
   ByVal bRevert As Long) As Long
Private Declare Function EnableMenuItem Lib "user32" (ByVal hMenu As _
   Long, ByVal wIDEnableItem As Long, ByVal wEnable As Long) As Long

Const MF_GRAYED = &H1&
Const MF_BYCOMMAND = &H0&
Const SC_CLOSE = &HF060&
Public Function EnabCloseBut(boolClose As Boolean) As Boolean
Dim hWnd As Long
Dim wFlags As Long
Dim hMenu As Long

' получаем hWnd окна Access
hWnd = Application.hWndAccessApp ' Me.hWnd
hMenu = GetSystemMenu(hWnd, 0)
If Not boolClose Then
   ' делаем кнопку серой, недоступной
   wFlags = MF_BYCOMMAND Or MF_GRAYED
Else
   ' возвращаем все как было
   wFlags = MF_BYCOMMAND And Not MF_GRAYED
End If
EnabCloseBut = EnableMenuItem(hMenu, SC_CLOSE, wFlags)

EnabCloseBut(False)