An occasionally occurring glitch/bug on the iOS version (all Apple products) of R Instructor exists. You know you've got the "bug" if after downloading R Instructor from iTunes much of content appears absent and the videos don't work. The solution: Tap the refresh button in the top left corner of the application. If you're not sure if you have got the "bug" or not -- hit the refresh button anyways, it can't hurt!
We have figured out the source of the problem but we need a little time to fix it. An update should be coming out soon.