When doing the "sheep" test (sheep.zip), you have to burn the files:
sdold.dat, sd251.dat, sd290.dat
on a CD-R with Nero restricted to ISO mode 1 (8.3 file names)
using your Plextor PX-716A burner.
Then try to copy back the files from the CD-R to your HDD using
a Toshiba SD-M1502 DVD-ROM reader:
a successfull copy back from the CD-R of
sdold.dat verify 1-sheep-writer
sd251.dat verify 2-sheep-writer
sd290.dat verify SafeDisc 2.90+ support
Have you followed exactly those steps?
Have you successfully read back all the .dat files?
Thank you for this much awaited info