I think your problem resides not with permissions as much as it does with the following:"Additionally, a 404 Not Found error was encountered"
Clearly the file has no ownership permissions if it does not exist. Sometimes, webhosts will mark an invalid URL as "Forbidden" so I would suggest checking your URL filepath.
This is just what I have observed through day-to-day usage. It really does seem like it is a permissions problem, but you said you already tried that
So this is my best guess without actually being at the computer.
Hope this helps you out,