Hi guys, sorry this is probably something simple but I'm at a loss!

I'm following the awesome instructions here to modify my BT2.iso file so that my new alfa will work better.
http://forums.remote-exploit.org/showthread.php?t=6784

bt2.iso boots fine before I change it but once I use poweriso and drop the 3 files in the modules dir, I get this error.

"ISOLINUX 3.36 2007-02-10 isolinux: Image checksum error, sorry...

Boot failed press a key to retry..."


What am I doing wrong?