Right! Note that the thread you pointed out was to the MLEP course, not DLS. I assume their notebooks work the same as ours. Note that there is a topic about this on the FAQ Thread for DLS that describes what Tom suggested in more detail.
Has this ever worked for you on any other notebooks in Course 1 or Course 2 or is this the very first time you are trying this on any of the course notebooks? I’ve seen a couple of cases where the problem was that the student’s account was in some kind of weird state. The solution was to talk to the Coursera Help Center and have them “unenroll” you from the course and then “re-enroll” them. If this is literally the first time you’re tried to open a notebook, then it might be worth doing the “unenroll” method.