An answer perhaps some years (!) too late, but since I encountered the very same error and searched Google for an answer to the very same question, I thought I'd just might add some words here now that I solve the/my problem.
I had 6 movie clips, and by removing one of them the ISO creation would work properly. So I thought there was something wrong with that one file and re-rendered it and its sound. No difference. So I tried to make it somewhat shorter, no difference.
But then I checked "Media Properties" for that file and clicked "Track Media". There it turned out DVD Architect had chosen the wrong file for the audio. When adding the movie clip to the project, I had selected the AVC file, like I always do, and normally DVD Architect will automatically fetch the corresponding AC3 file while at it. This time around, I had an MKV (with the same filename as the AVC and AC3) that I had created to watch the rendered video before I had time to compile the disc. And this MKV file had been selected as the audio track file.
Next to the audo track file there was a pulldown menu icon, and by using that and "replace", I could set it to point towards the correct AC3 file for the audio, and voilà, now the ISO is properly created.
Good for me, and hopefully it can help someone else.