We upgraded to Moodle 2.9 when anyone clicks signup to a course we get a web page unavailable message.
The managers email still goes out, but the course tutor email no longer goes out until they have been approved, we had it set so the tutor got an email to approve
The page trying to load is the confirmation page.
We've been upgraded and working with it for months and none of the users have mentioned it as it mostly works, they just need to refresh.