I updated to version 2.6 from 2.5.3 and it seems like it works fine in every other way, but when I try to open any existing lesson I get "missing YUI3 module details" I have not tried to create a new lesson to test it - I was more concerned with getting my site back up. I see that MDL-21480 addressed a similar problem in version 2.0, but I have not had a problem until now. I had to revert back to my backup to keep my server live and am afraid to try an update again until I understand the problem and how to resolve it.