I setup a security group for content editors. I gave them certain permissions as seen in the attached screenshot.
When a user logs in, they are brought to the admin section. As soon as they click on another page, a dialogue box pops up saying they have been logged out of the admin area, and they are directed back to the login form.
These are just basic pages. I also noticed that pages that have images associated with them with an ImageField, they can't view them. When they click on the tab, it says they don't have permission to view it, and a login form appears in that iframe.
I'm having a similar problem with users with limited permissions being constantly logged out. The only documentation I could find is at [url]http://doc.silverstripe.com/doku.php?id=permissions:codes[/url] and it's not terribly helpful.
I encountered the same problem and submitted a bug-report for it. A possible solution can be found in the bug-report (somebody submitted a patch already): [url]http://open.silverstripe.com/ticket/2769[/url]
Edit Just for clarity: The mentioned bug-report addresses the issue with permissions on iframes for file-uploads.