It could be a matter of what media you are using. I had a similar problem with some DVD-RW discs (not in the Mini, just in general). One brand I picked up (FujiFilm I think) would work find in my DVD-RW drive on my PC but I couldn't read them anywhere else (even a newer DVD-ROM drive I had). I ended up picking up some Ritek DVD-RWs and they worked fine everywhere I tried them.
So you might want to see about picking up a couple CD-RW discs from a couple different makers. I think the ones I have at home that I've never had any trouble with are Imation. But they're pretty old an can only be written at a maximum of 4x.
This might be a good time to start up a CD-RW compatibility thread so people can list what discs they have an whether they work. (assuming this doesn't already exist)