Comment 1 for bug 743817

In my case, I encountered this issue with Ubuntu x64 alternate 20110329-1. I was installing off a USB drive, and my laptop has no CD drive at all. If the error intended to indicate that it was not able to mount the installation media, it should say so (and as Bruce has noted, makes very little sense, since the installation itself had booted off the media). If it intended to indicate that no physical CD drive was available, this would seem to be a problem, since my laptop has no CD drive and could not possibly add a CD drive just to suit the Ubuntu installer.

Alpha 3 does not exhibit this behavior when using the desktop/Live CD install through the same method.