I received a burned disc and popped it in the Panasonic, but it wouldn't play and I got a "U99" message. Disc wouldn't eject, the recorder wouldn't transmit TV channels at all. I read the U99 threads here and followed the Panasonic site's recommendations (Power off button for 10 seconds/unplug/wait 1 to 5 minutes/plug back in). I got the expected "Self- Check" message but the U99 message appeared as well and again the unit wouldn't eject, play the disc or TV channels. I ended up taking the cover off, taking a black plastic top off the actual DVD drive unit and physically removing the disc; after that everything seems OK. BTW, the disc that caused the problems was a Playo DVD+R. I personally use DVD-R's, but I would swear the Panasonic HAS played some +R discs and, at worst, has messaged that the disc was unplayable. This was the first time the unit ever locked up like this. I'm not sure I would advocate opening the unit, but others may become as desperate as I was.
That's a new one on me. I have found that the unit usually reads finalized discs as "DVD-Video" and has no problems. I haven't used DVD+R, but my unit has played back DVD-RWs, which it also won't record. The quirk mine has is that DVD-RAMs recorded on my computer are read by the Panny as "unformatted". No lockups, thank heaven.