The quality of DVD will likely have a major impact, given that the readers in the cars are often finicky. I'd recommend Taiyo Yuden DVD-R (media ID TYG02, preferably) discs. I think you can get them from Amazon. DVD-RWs are often less compatible with all sorts of DVD drives.
Make sure you're burning the ISO properly with imgburn. Either associate the file type with imgburn so double-clicking it causes imgburn to open, or do a file>open with imgburn. Burn at 4x or 8x and select the "verify" option in imgburn so it will check if the burn is valid.
| 335i coupe | Monaco Blue | JB4 G5 ISO | Style 313M | Huper 40% tint | Aero lip | CSL trunk spoiler | M3 sideskirts
| Paint-matched grilles | Painted reflectors | GP Thunder II angel eyes | Smoked LED sidemarkers | Self-coded |