Two things: When you log into the course, you are automatically logged into the Request/Message Board. The Request/Message Board logs you off after 24 hours, but you are still logged into the course.
If you have been on the system for over 24 hours, the solution is to go to the course index and log off using the link at the top right. Then click back to the course and log back in. Fixed.
If that doesn't fix it, re-start the computer and start fresh. Problem solved.