I'm having similar problems; it won't let me download or listen to any audio. PDF's work fine, but for all audio I get an error (in Opera) and a 'source file could not be read' dl error in Firefox.
edit - mainly for the newest lessons (Newbie S4) and some older JCC 31+. I'm having no problems downloading UI 6+, so I'm not sure what the problem is...could just be a site error.
Though I'm not sure why, the downloads all seem to be working today. Looking over some other tech-support posts, it looks like people that have this sort of problem find everything as normal about a day later. I hope you find the same is true for you, AJ.