handling online courses

I'm looking for input on how to handle online courses.

A bit of background:

Courses are built with XML in a CMS system. These are published to a database and then interpreted by a asp.net website. On the website users register and take the course. Some of these courses are very long (16 hours, more with the required reading) and consist mostly of different types of questions (multiple choice, single correct, multiple correct etc) and a scoring to enable pass/fail. Due to the length of the courses, many users take up to a couple of weeks to finish.

The problems occur when a user is half way through a course and it is updated and republished from the CMS system. If the number of questions has changed, the user may have already passed the point where a new question is inserted, this will affect his score. The scoring might have changed directly and all sorts of mischief.

So, any tips on architecture and patterns for designing a course that can be modified by the author without disrupting sessions that have already started?