Thanks a lot for the replies and useful advice.
The most interesting thing is that the DVD-Rs 8x (Taiyo Yuden) have the same problem in both of my standalones: Philips DVP720SA and the Pioneer DV-575A. Both Players are one of the best in their category and reading all existing type of media (checked). Both of them having problems only with -R burnt at 8x (media burnt at lower speed are played without any problems, as I have mentioned earlier). All DVD+Rs (RICOH, ProDisc) burnt at 8x are played flawlessly in both players. Interesting because Philips prefers "+", Pioneer prefers "-", as we all know.
1. I wanted to watch one of my older backups burnt on Sony DVD-R (Mitsubishi Chemicals) with Matsushita UJ-811 at 2x. Result: freezing, skipping at the end of the backup (???). Played flawlessly in my ex-standalone Daewoo DV 1091 (???).
2. DVD-Rs (Taiyo Yuden) burnt at 8x and skipping, freezing in both my standalones played flawlessly in PS2 as well as XBOX (???).
3. Burner used: Toshiba SD-R5272 (ver. 1031).
4. Software: AnyDVD and CloneDVD2 (both latest version).
Zevia: Yes, it is a Pioneer in my sig (great player, btw).