When your screen freezes while completing a lesson
-or-
If your work is not being saved
Chances are, you've seen this message when you logged on
This is caused by the existence of an already active session for your username on the server. It is usually a result of exiting the system without logging out (i.e. clicking the x in the upper right corner of the window).
To resolve the issue choose ‘proceed’ when you get the "user is already logged on" message shown above, but then immediately log out by clicking on the file menu and selecting logout. This will terminate all active sessions. You can then log back in and should not see that error come up again.
NOTE: If you choose proceed and continue to work after seeing this message, your work will not be saved, and you will likely see the system lock up or freeze while you are doing your work.