I've had this happen once or twice too. It happened to me when I was trying to import a couple of heavily propped figures into Bryce5 from Poser4. The best I could guess was that some of the props were not OBJ files originally, but rather 3ds or some other format. So when Bryce was trying to import them as OBJ's it went "Huh?", hence the I/O Bad Media warning. You might want to post this in the Poser forum as well, in case anyone there knows what it is.