I don't know what the answer is, but I've got exactly the same problem. I was recording something and I got a U88 message afterwards. Ever since, neither the disc that I was using could be recognised, and no other disc is recognised either.
I've also tried a DVD lens cleaner disc, but it doesn't recognise that either!
The frustrating thing is that I haven't used the recorder all that much, so I'm reluctant to buy a replacement. Surely there's something that will fix it!
Michael Harker, February 2010