Hi Mike,
I have a similar issue with courses in Moodle 2.6. When checked in Moodle Tracker, I was asked to upgrade to the latest build.
However, based on your post, I set "Student Skip Content Structure Page" to Never for the courses that failed to work before, they seem to work fine now.
Just want to know if this setting would help or as suggested in Moodle tracker, should I go for an upgrade to the latest build?