Hi Liz,

By default the only enrolment plugin that is enabled in a new course is Manual enrolments where the course administrator has control and has to manually add each user that has access. Other enrolment plugins - self-enrolment, program and plan enrolments, audience enrolments etc - have to be turned on for each course. This course also looks to have Audience enrolment turned on. But if a learner is not in the Audience then they cannot enrol in the course. Is that what is happening here?

Basically if a course event is going to be advertised on the site-wide calendar, then everyone needs to be able to actually enrol onto and access the course, the simplest way is to activate self-enrolment.