Popup error when showing calendar block on enrolment page

Steps to reproduce:

• Visit the site home page as an admin
• Add a 'Calendar' block to the front page
• Set the block page contexts to 'Display throughout the entire site'
• Create a course
• As a non-admin user, try to access the new course
• You should be redirected to the enrolment page for that course, with the calendar displayed.

Expected outcome:

• No course calendar events displayed, no error messages

Actual outcome:

• No course calendar events displayed, popup error: requireloginerror - Course or activity not accessible.

Clearly the login check is correct, because the user is not allowed to view calendar events for a course that they are not enrolled in. However, the popup error should not be displayed as this is confusing to the end user.