Ok a strange situation, I have costume attribute (of type file) set for a page that I want a non admin user to be able to update.
When I log in as the user I get a strange behavior: I can add the attributed if it hasn't been added yet and upload a file and choose it, however after that is set I get "permissions denied" on that attribute and can't edit it, even if I remove the property and choose it back I get the same.
My permission setting
The user can view and add files (file manager properties)
User can view and edit page properties with the file property checked
User is the owner of the page.