Units are not showing for students

When a new person creates a new account for enrolling in a course, he can enroll successfully after registering a user account.
After that, when he goes to the Units section, it says "No visible units in the course currently. Please check back later". (https://m4****y.com/courses/no20*****************ent/units/)

But when I check that page as an Admin, I can see all the units fine. Can you help me find out what is causing this problem?