You are correct you would have to make an iso when using shrink to burn with decryper using iso mode ....but like me you make video_ts and audio_ts folders and burn with nero
@PC-GUY nero is great for just this job .. sure it sucks for encode but just burning VIDEO_TS and AUDIO_TS as a dvd video disk then its good its done me well for the last couple of years (note for reference decrypter uses nero burning engine anyhow )
I would put this down to a media problem a program such as DVD IDENTIFIER will give the media id and maker
my suggestion would be TRY different media such as one with RITEK G05 dye on it if possible get REAL RITEKS
my other suggestion would be BURN SLOWER i don't know what speed you are burning at as you did not mention it in your posts its quite possible you have a bad batch of MEMOREX and some will burn fine at the rated speed on them and some will only burn at SLOWER SPEEDS ... you may get some that do not burn at all
let us know how you get on