If you knew the Media code of each Disk burnt that would help you understand what your standalone player likes and not like.
If you are using +R's are you using bit-setting? was bit-setting turned on or off when you burnt each of the +R's?
To give us a better idea, could you give some spec's
- Model of your standalone
- Model of DVD burner
- Media Code of your +R's
I believe that CloneDVD auto set bit-setting for +R's DL? to make them more compatible, not sure which version started it