CANNOT FORCE PRIVATE on 4.7.

There are a problem at the filemanager settings area.
I click on "Force Private" on both areas: General and Attachments and hit SAVE.
Then appears the same page, with all the rest saved, but "force private" not selected.

File areas
Area Descripción Max size (Mb) Force Private
General All files not specifically stored in another area.
Attachments Area where all node attachments are stored.

Questions:
1. Are those areas created by default? Can I change them?
2. At settings I have set the upload to "private" and disabled the "upload" module. Is there aything else that I should do?
3. I can upload files, but they are not private, they are accesible by all.
4. What should I put on:
Public File System Path
Public File System URL
Private File System Path

Thanks in advance!!!
I dunno what else can I do to make this module work. And I need it desperately!

Rosamunda