Ok, I realize a lot of other people have had this problem and somehow managed to resolve it. I have done a lot of reading and experimenting but so far NOTHING has worked. So, to recount everything that I have tried and all the details to this problem:
First of all, I would like to mention that I have successfully burned a number of DVDs in idvd in the past. Then suddenly it just stopped working.
I have run a verify/ repair disk permissions. I have deleted all the idvd files off my computer, the .plist and preferences file, restarted, and reinstalled iDVD TWICE with a custom install. I have 500 gb of free space on my boot drive. I used a cleaning disc on my SuperDrive, and my regular DVD player. I switched to a better brand of blank dvd. I am now using Sony DVD-r, 4.7 gb discs although memorex DVD+r always worked just fine before. The project I am burning fits on the disc. I am not using chapters. I tried turning on the tv safe area and made sure everything was inside it, but still the same problem. I tried booting up in safe-mode then restarting. Still, same issue. I am burning at 2x speed, using professional quality setting. The project preview works just fine. It goes through the whole idvd process just fine, until the burning and multiplexing. After burning about 10 minutes of the project, the disc ejects suddenly. Idvd says "done" but then at the bottom it says "about one minute left" and the little burning wheel symbol is still spinning. The disc plays fine in my DVD player till about ten minutes in, then freezes and eventually goes back to the main menu. I can see on the disc that it is only partially burned.
Oh, and I have also tried saving to a disc image and burning with toast and disc utility. Once, this actually did work with toast and resulted in a playable DVD. The weird part was that I still got the error sense key message in toast and thought I had made another coaster, but when I tested the DVD it worked fine in my regular dvd player only (it was not readable in my xbox or ps2). Since that one fluke, however, it hasn't been successful. Disk utility did not work for burning the disc image. I am absolutely at a loss here...somebody PLEASE help.