Tony, slow down mate, I got to go and have a sleep... Besides, I am no expert, far from it - However:
>>But now, if I log in as some user who is friends group, then I can access to primary ibay too. But I can't write there or do something else. But I can view files - this is bad. Can I do something to repair this?
This is Ok, logging as a user for ftp opens the whole box. You can access a lot of things, but cannot do much in terms of write/delete BECAUSE, taking as an example the case of the primary site, it is created and owned by admin. Other ibays or directories are owned by other entities, you will have to log as this precise entity to have write access. Linux protect itself, and just as well, or begineers like you and I would demolish their system in no time at all... So if you want to change the content of your primary ibay, log as admin, and all will be well. Become familiar with permissions for directories and files. Note that sme comes with midnight commander, type mc at the command prompt, navigate your way to a directory of interest, then F9 to drop the menu, go in files and select cHmod - it will tell you who own what, and allow you to change permissions - please be careful!
Note: ftp is not a secure protocol. Check sftp please if you intend to open your box to the world...
>>So, I installed this rpm dungog-proftpd-chroot-0.1-3.noarch.rpm and I think this is the rpm that I need. But when I do there changes (Global changes) and then push the Restart FTP server, then i get Internal Server Error and my changes won't change.
Let me check this and come back tomorrow. What version of sme are you running, and how did you install?
cheers

chris