Media error and extremely confused

[stagands]

We've been trying to burn a rather long DVD movie of a recording of a show we just did. The movie file was edited in Final Cut Pro 5 and has a final length of 2h27m. After compressing the video and getting the resultant .m2v and .aiff files, we put it into toast to burn. Due to the length, we are using DVD+R DL discs. About halfway through, we got a write error saying there was a problem with the media. We tried to burn the disc image from toast, which worked successfully, but then when we tried burning the disc image using disc utility, it got all the way to the end before ejecting the disc and saying media error as well. This is really frustrating. Help?

Mac OS 10.6.7
Optiarc DVD RW AD-5680H
Imation Double Layer DVD+R DL discs
Toast 11 Titanium

Thanks!