Content Modeling

Hello! I'm having problems with the import of "Content Modeling". I'm adding to the PackageDefinition the Forms, the ItemTypes and the created relationships in the ItemType from the Referenced Type in the Element Binding, as well as the Content Modeling it self. The export is fine. But when I try to import, I get an error that an "ItemType with this name already exists" for every Element or Property type. Has someone encountered this kind of problem and can you suggest a solution for it? Thanks. Emi