There are two possibilities: one is that the course has ended, and the other is that there is a problem with the massive open online course system.

The first one depends on whether this course is over and the next one has not been taught. If not, please log out and log in again.

It may be that there is something wrong with his updated system, which makes it impossible to enter the course now. Personally, I suggest you uninstall the original again before opening it.