I don't know what to tell you other than check the forum faq section, but the procedure to burn a BT ISO onto a DVD is pretty much the same as any other iso.
Make sure you burn at the slowest speed possible something like 1 or 2 X is generally recommended. Also ensure download md5sum is correct before burning.
Try using different brands of DVDS.
Again check the faq section for more info. This has been covered.