Ok, the pot you need to tweak is the left hand one of the two pictured below. It is the one closest the sloped ribbon cable thingy. By turning this 1/8 turn clockwise my drive now reads everything i chuck at it, even the cheapst of cheap cd-r's .
I'm not 100% sure that the dvd is the problem cause I have burned the same game using nero with same settings, same media and one will work and the other won't.
I have had a similar problem like this. It is probably caused by using either/or cheap dvd media or cheap dvd writer. I use a LiteOn writer, pretty cheap but also pretty poor at producing high quility burns. For PC use it is fine but when mixed with the xbox things aren't so great. One thing that does help is burning at the slowest speed possible, 2x in my case.
Hope this info helps ya a bit.