Non EU citizen working in Belgium

Can anyone point me in the right direction to obtain a work permit for a non-EU citizen to work in Belgium? My company is looking to offer a traineeship to someone from Croatia and before they can apply for a visa it seems we need permission to offer them the traineeship but none of the Belgo-burocrats can tell us how or where we can obtain the permission although they can ll tell us it is required. Permission has to be granted in advance of the visa apllication but how?