I found this from time to time, when others had no problem - I even mentioned a reason why this may be a few days ago. It seems +r has slightly less space than -r (thanks to someone who posted the actaul info - it's approx 50MB's-10MB's).
This is why an image may burn to -r but not to +r. As suggested, you can mount the image with Daemon tools and extract the contents, then try burning that - or use Isobuster to extract the contents and once again try burning that.
Often an image file is much larger than the contents - I believe it's ISO's that have this problem, and nero will often (for me onto +r) not burn the image, but if I extract the contents to HD and not delete anything, but add the contents to a blank dvd template in nero, it's burns the files just fine.
Food for thought.