When quick enrolling on a course, you will not immediately get access to the course’s files.
If you try to upload an attachment to an item before you get access to the Course Files area, you will get a cryptic error message.
You can tell if you have access to the Course Files by clicking on Content Collection in the Control Panel.
If you don’t have access, you won’t see the course ID (eg 2019_LE2103) listed.
Rather than wait five minutes, log out and back in again.
There’s more detailed information on Behind the Blackboard.