If you have upgraded to the iOS app 2.0 on your iPad and are getting the error "The requested URL cannot be found on this server" please see below for more details...
Streaming Only - No Downloaded Lessons
If you are streaming only (with no downloaded lessons), please delete the app and re-install the app from iTunes to resolve.
Downloaded Lessons - Upgraded from v1.0 iPad app
If you had lessons downloaded in the original app 1.0 and recently upgraded to v2.0 then most likely not all the files fully downloaded on the iPad 1.0 app - for example the jams or PDFs did not not fully download (which was a problem in the original app).
Log in to the iPad 2.0 app and go to My Course, select the course in question.
Toggle the icon to Download All on the course to download the remainder of the files. It will not re-download already downloaded files, simply complete the download process for any materials (assets) not yet downloaded.
Or if it is just one individual lesson within a course, you can delete an individual lesson (click the 3 dots to the right of the video) and then re-download.