i've had some weird and wonderful things happen when scanning with my liteon ltd 163 dvd rom drive.
honestly out of all experience, liteon dvdrom drives do not cut it for scanning dvd-r media.
i've purposely have gone out and bought a 451s drive just for scanning believe it or not. (I am not fortunate either, so don't say anything those lines)
the ltd163 drive scanned a disc with results of 900 max pi and 800 po where the same disc scanned in my ldw451s scanned 18 max pi and 9 max po. these results speak for themselves. I continue getting tracking error failures on the ltd163 drive as well. where the 451s drive does it without a hickup with a nice scan. (keeping in mind that these are taiyoyuden 2x dvd-r.)
i myself own a 106d drive which i use purely for writing and the 451s for scanning. i have not really attempted writing in the 451s yet, but will do shortly and hopefully get the 851s firmware placed into it.
hope this helps with your problem.