Have you tried setting output to the hard drive, then burning separately with ImgBurn?
If you have ImgBurn installed, you can also set DVDFab to use it as the burning engine. Common Settings-->Drive-->DVD Write.
But it sounds like you might have other problems in the system, and this might not be a DVDFab problem at all. Do you have issues burning anything outside of DVDFab? Just try a burn of some data using ImgBurn.
Also, I'd recommend using Verbatim brand discs. Get the ones with AZO on the label, not the "Life Series" Verbatim discs.