This article is from the Mac Programming FAQ, by Jon Watte email@example.com with numerous contributions by others.
The Menu ID as used by the menu manager is NOT the same thing as the
MENU resource ID (used in the MBAR resource and with GetMenu()) When you
create a MENU, ResEdit sets the menu ID to the MENU resource ID, but if
you re-number the resource, you will have to open the menu in ResEdit
and change the menu ID using the "Edit MENU ID" menu item.