Has it ever happened to you. You burn a coaster on an RW disc and then the drive will no longer even accept it as an RW disc?
I had it happen to me on a Memorex 10X CDRW. (This was part of a rotten batch that for some reason would only burn at 8x) The burn seemed normal, but after burning and trying to access the disc, XP gave me the old "Please insert a disc into drive D:" So I tried to wipe it with Nero and it said "Please insert RW media", ok so I tried Ulead DVD Studio and it gave me the same error, cdrecord...same error.
The amusing thing about this is I've seen worse IMO situations that it could reformat.
I had a person open a service ticket once several years ago, because they couldn't read an RW disc after burning. I went to their desk and saw a big (thick) fingerprint on the disc. It was almost like someone who just ate something really greasy picked up the disc. I wiped the finger print off and the fingerprint was actually traced in the media. (Which was actually cool in a way) The laser couldn't cut through the finger print so it became outlined. I popped the disc back in and did a long format (this was when RW media was about 5$ a disc), came back an hour later and the fingerprint was gone. And the disc was perfect again.