The fact that you can back up some of these discs is meaningless. The fact that the name on the label is Samsung is also meaningless (what is the Media Code on these discs?). The fact that they were recorded using Nero, and that you used the ISO method is also meaningless.
In fact, even if the disc plays fine in most players, this is also meaningless (since most players ignore very minor flaws and errors and gaps in information, while the ripping process is going to stop and let you know about each and every missing "1" or "0" that it encountered. Most players will just skip past these, and do the best that they can at displaying the image, even if it jumps or skips.
My best guess, based on the information you provided, is bad media. Those other discs may (or may not) be living on borrowed time, since people have found that there is a lot of stuff out there that seems to gradually begin to deteriorate after months, or within 1 - 2 years.
Do a major search on "best cleaning methods," and try repeatedly. Note--> Save the toothpaste methods for a "last resort," since that can be more destructive.
If you have other DVD drives you can use, try them (sometimes one drive will choke on bad media, while the next one will not). Upgrade the firmware, since most firmware upgrades "teach" the DVD device how to read some of the less than desirable crap that is out there in the market (and there is more crap than there is decent stuff). If you have friends with PCs, ask if you can let them give it a shot, since their particular DVD-Rom or DVDwriter drive may be a bit more tolerant than yours is. (I have three DVD drives hooked up, and there have been cases where one drive choked, while the others did fine. There have been cases where TWO choked, and the third one read it fine. There have also been a few cases where NONE of the three could handle the source disc.)
Best of luck...