maybe it has something to do with bitsetting raulpica mentions although I don't really know what it means.
You have already burned something and it worked, right? If so, then it's not a bitsetting problem, forget about it
Try to find XBOX Backup Creator and try burning the .DVD file (it's essential, as it has the LayerBreak defined in it)
Oh, BTW, I just remembered that my DVD file wasn't pointing to the file correctly.
Open it in notepad and try to see if it's like this:
CODELayerBreak=1913760
image.000