Problem Burning DVD+R DL w/ DVD Architect Studio 3.0

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I have successfully been creating single layer DVD+R movies using DVD Architect Studio 3.0 but I recently rendered a movie that was too large for a single layer DVD, so I borrowed a friend's external DVD+R DL burner.

I am having trouble though at the burning stage. Everything proceeds correctly up through the "Burn In" stage, then all of the sudden the burning of the actual movie happens almost instantaneously and the "Burn Out" stage begins. Obviously the movie is never being burned to the DVD+R DL (and I have created 3 coasters so far with these expensive dual layer discs).

Does anyone know what the problem is or what I am doing wrong? I changed the disc setting in Architect from 4.7 GB to 8.5 GB, which is really the only thing I have done differently from when I successfully burn single-layer discs (other than the fact that I am using my friend's external DL burner).

As stated above, I am using DVD Architect Studio 3.0 and an LG External Super Multi DVD ReWriter (model # GSA-E10L) hooked up to my computer via USB. And I am using TDK DVD+R DL discs.

Any help would be great, thank you!