Simply replace
SELECT ...
FROM course, course_event, course_event_package_links
...
WHERE course.course_id=course_event.course_id
AND course_event.course_event_id=course_event_package_links.course_event_id
by
SELECT ...
FROM course
JOIN course_event ON course_event.course_id = course.course_id
JOIN course_event_package_links
ON course_event_package_links.course_event_id = course_event.course_event_id
...
About your error message, are you sure course.course_id
exists? Maybe it was replaced by course.course_code
?