procedure TForm1.SetCloseButtonEnabled(const Value: Bool);
var
hSysMenu: HMENU;
begin
fCloseButtonEnabled := Value;
hSysMenu:= GetSystemMenu(Self.Handle, False);
if hSysMenu <> 0 then begin
if Value then
EnableMenuItem(hSysMenu, SC_CLOSE, MF_BYCOMMAND or MF_ENABLED)
else
EnableMenuItem(hSysMenu, SC_CLOSE, MF_BYCOMMAND or MF_GRAYED);
DrawMenuBar(Self.Handle);
end;
end;