When we install on a v7, we get 1 in 4 or 5 that has this problem, usually with DVD-R. Your installer should check and set the laser azimuth (see the FAQ in
www.ps2newz.net for instructions).
Sony set some v7s badly in my opinion so that originals read but not backups. Your burning practice is perfect.
By the way, when you go to DVD-R, we find that those v7s are then ONLY happy with Traxdata DVD-R.