Working with blu ray isn't always cut and dried, unfortunately.
And no, there isn't much to go on there, except that the AC3 audio setting is on 640kbs, which is not within dvd-video specifications. It can't be more than 448kbs for dvd-video, but jdobbs knows this and it should convert to this amount or less automatically when going to dvd-video. If you are a member of doom9, you should post in jdobb's BD Rebuilder bug thread: http://forum.doom9.org/showthread.php?t=143716
The video encoding completed so you should have a copy of the video stream somewhere. That is the main section in time spent converting. Make certain that you have this .m2v file.
Assuming you have it, I'd go back to the original blu ray that is decrypted on the hard drive and use Clown BD to extract the audio stream. To do this, you import the blu ray movie into ClownBD, let it analyze the movie, then deselect everything except the main audio stream that you want to save. At this point, you'll also be able to see what type of audio is in the movie. Set Clown BD to output as m2ts files, but also set ClownBD to convert the audio to AC3 at 448kbs or less. Start the conversion. You'll get two files as output, an m2ts file you can safely discard, and an ac3 audio file.
At this point you should have a .m2v video stream and an audio stream that is dvd compliant ac3. If Clown BD failed in the conversion, we have more problems. Try extracting without converting to ac3. This audio stream won't be compliant, but there are other tools for conversion.
One tool for this conversion of the audio stream is Audacity 1.3.14 beta (with the ffmpeg plug-in!!). Import the audio stream, change project rate at the bottom left to 48000 HZ, then export. Use AC3 as the export codec and set bitrate to no more than 448kbs. This part gets a little tricky however, since I don't know the size of your m2v file, and I don't know what bitrate BD Rebuilder was originally set to use in the audio. It is possible that the combined size of the two streams will be too big to fit onto a dvd-video.
Assuming you haven't given up by now :), you import the .m2v file into AVStoDVD. Right click on the .m2v file in the main window of AVStoDVD and add audio, which is where you import your newly made audio stream (from Clown BD or Audacity, whichever one you had to use). Check the Preferences in AVStoDVD and make sure you are making the right size dvd (DVD9), NTSC instead of PAL, and that both video and audio streams are kept intact if they are already dvd compliant. You should also check the bitrate for the ac3 audio setting and make sure it matches what you want. Save the Preferences, and make the dvd.
If all this sounds complicated, it is. BD Rebuilder doesn't fail that often when making dvd video from blu ray, but when it does, the alternate paths get a bit convoluted.