I'm having the same problem! I opened a support ticket with Roxio on the Feb 5...no response as of yet. I can burn shorter files just fine, but I have a couple of files 1:28, and 1:32 long. They both fail after encode prior to multiplexing. IDK if the encode fails to complete or the multiplexing fails to start. I am using Toast Titanium 17.3 on a Macbook Pro with macOS Mojave 10.14.3. I can burn the same files with my iMac OSX High Sierra using Toast 12. What's changed?