depends on how your app is constructed, but be aware that even if you have disabled the close button property it is likely the user can still close the form by either right clicking on the form window titlebar if using overlapping windows or popups, tab if using tabbed documents or the access window titlebar. Or by closing the app from the windows taskbar or task manager.
So you also need to include some additional code and a form scoped variable. Something like
put this at the top of your form module before your first sub or function
Code:
Dim OKToClose as Boolean
in your close button event use
Code:
OKToClose=True
docmd.close
and in the form unload event put
Code:
if not OKToClose then msgbox "Please click the close button to close this form"
Cancel=not OKToClose
however not sure if that will work for taskbar or task manager