I was trying to encode a project to mpeg-2 DVD yesterday, when I repeatedly received the message "Error compiling movie. Unknown error." I had had this happen before and I can't remember what hoops I jumped through to fix it. But yesterday, I found a simple solution that may work for someone else in the future should they ever search for this problem in our forum.
The problem turned out to be with some .wmv files mixed in with all the other .avi files I was using. And the solution was to right-click on the .wmv clips in the project bin, choose "modify," then choose "interpret footage. From there, I changed the frame rate choice from "Use frame rate from file" (which was 30.00) to "Assume this frame rate" and entered a value of 29.97. Voila! Everything rendered without a hitch!