Has anyone else had any problems with Zero Defex media?

I authored 4 discs about 8 months ago and they worked fine. I left them on a spindle and yesterday tried to play them, in both my PC player and standalone they do not read. They are not scratched so I can't work out why they don't play.

Other brands of media play fine, just these Zero Defex discs that seem to be bad.

Am I alone with this strange occurance?

Thanks,

Rob.