That "Unable to Write Chunk File" error can still occur in the current version of Audiobook Builder but for reasons unrelated to what this topic discusses. The best way for us to learn more about your unique situation is to see a System Information/Profiler report generated just after the issue occurs there. You can create one of these reports by clicking the Finder icon in your Dock, going to the Go menu at the top of your screen, clicking the Utilities menu item, opening System Information.app (or, System Profiler.app on older OS's), then going to the File menu and clicking the Save... menu item. Attach that file to an email sent to
support@splasm.com and we'll have a look! If your M4A file is small enough to email, perhaps send that on over as well, if you don't mind, and we can also test with that.