I've had this problem as well. I got the same error message from 2 pcs (both laptops), but then booted successfully from my desktop. I've managed to get round the problem using Smart Boot Manager - download from http://btmgr.webframe.org/ and burn to cd. To boot:
1) Boot Smart Boot Manager
2) Scroll down to CD-Rom on the menu, but DON'T hit return
3) Eject the CD and insert your Live Puppy CD
4) Wait until the drive spins up and then hit return
Puppy should then load (well mine did - I'm writing this on the laptop I booted using the above method). It's something to do with Eltorito CD Roms, but I can't remember what offhand. I had the same problem with Kanotix when that was upgraded - one version wrked, the next didn't.