try your DVD+Rs. If both brands dont work then its the media. Most likely it'll work but i think common consensus seems to say that over time DVD+Rs will wear down the dvd drive.
i noticed with my softmodded wii, I cannot use plain dvd+r, but if my bitsetting is on dvd-rom for +r, then it will work.
proper setting [booktype] on burning software definitely helps. :)