Nah. I just upgraded from Toast 8 to 10.0.8 directly. And guess why I'm searching these forums? Yup. 18771 error. About half my files have this problem. For me, the fix is to simply switch the encoding to mpeg 2. But that' s a cruddy workaround because it's ridden with small noise and artifacts compared to the the mp4 encoding.
But I absolutely have the 18771 error with 10.0.8. You might just be getting lucky. I'm encoding 1080p or i ProRes files from FCP. Sometimes it works, sometimes it doesn't. But it is consistent on which files it won't encode. It's just flat out ridiculous. They've been charging for this feature for years, and if you look back through the threads, over 2 years ago you'll find roxio employees stating that they're "working on it" so I have no confidence they even know what the problem is or better yet how to fix it. Bummer. Been using Toast for nearly ten years and they seem to have lost their way.