it could be a corrupted media table in the firmware, have you reflashed your drive at some point?
I had a similar problem when I reflashed my A05 with a particular firmware, one of the media recognition id's had been removed from the media table and I was left with a box of 5 unreadble/unwritable discs. Good job I have an A04 in work which still burns them
if using different software doesn't fix the problem you might want to consider flashing the firmware with a new version, the pioneer page at rpc1.org is a good place to start
look
here