I have the same problem -- the Adept manager and "Add & Remove program" disappear from the menus. I believe this is a bug as a result of instally RC1. Does anyone know if some modules got uninstall and fail to reinstall?
In RC1 and the eventual linuxmce-0704 release version Adept has been removed and all updates etc are handled directly by linuxmce. I think this is a temporary solution to the problem of the automatic Ubuntu software update mechanism breaking some of the functionality inside linuxmce by updating packages behind lmce's back.
You can still use apt from the console though and you can change the sources.list if you need to.