@vcarmer Welcome! Have you tried having the students go to their dashboard (or alternatively, your Canvas URL) then navigating back to the course? Sometimes when users log in and there was a change in a course, they'll get that page, but navigating back to the dashboard then to the course usually fixes it.
The other thing I would check is the 'student view' of the course to ensure that students are able to access the pages needed. Maybe someone unpublished something and they're trying to directly access that link?
Without more information it'll be hard to troubleshoot using the forums. You may want to contact your district level Canvas support for assistance with this issue as well.