need more info.
on hard to do titles do the movie only using both clonedvd 2 + anydvd
what media are you using? (try Taiyo Yuden and or Verbatim is your best choice)
and what is your burn speed? (if your having playback problems try burning at 4x and never faster than 8x)
do you have the latest firmware update for that Plextor drive? (check Plextor website to see)
also are you burning on a clean machine? (doing disc cleanup and defragging often)
don't run other programs while transcoding/burning unless your running a dual-core CPU