I just double left click the .iso (it has its own file icon when you install Nero or DVD Decrypter) and Nero comes up, then I burn. Are you dragging the .iso into Nero burning ROM? That might be the problem, Nero might be rejecting it becuase it thinks the file system in the .iso is incompatible, instead of just burning whatever is in the .iso. If you install DVD Decrypter (nice program btw ) or IMG Burn, all you have to do is right click the .iso, then click 'burn with DVD Decrypter" or something.

I think the whole reason DVD-Audiofile creates an .iso for DVD-Audio is because so many burning programs can't burn DVD-Audio discs in the proper format that will be recognized by DVD-Audio players. Nero screws it up if you try to burn a UDF ISO in burning ROM from .AOB files, and the disc won't play in the player. ONES will burn .AOB files to a DVD-A disc and the disc will be recognized by the player just fine though. With an .iso file, the burning program just burns whatever files and file system that are specified in the image file (.iso), so no chance to screw things up.