....
But I don't understand why this problem with unit names
Do you mean you don't understand why you cannot use the same name for different things ? Or you don't understand that they are different things ? I think its important that you do try to understand these matters, you will have a lot of problems (with any programming language) as long as you have not fully grasped the ideas there.
Maybe re-read my long and boring post and perhaps come back with just what part is not clear ?
Davo