Jacen, sounds like you haven't authorized the BluRay plugin yet. That is step one. It's not totally intuitive on how to do that, but it *is* step one.
Jim, there is likely nothing wrong with the file. I know you're a PC user, and likely mistrust Mac applications, but FCPX is a great program that outputs usable files. The problem is MyDVD. It will only accept certain files using certain CODECs. What are those files and CODECs, you ask? Great question! Sadly, Roxio has never answered. Through trial and error (and error, and error, and error, and . . .), I've found that it accepts only .mov files (see here).