Why would YouTube say your username is invalid everytime you register?

because with certain video programs, it makes the extension different. For example, the movie you are trying to upload may by a .flv video instead of a .mpeg - if you have a choice, change the extension to an mpeg. All the movies that i have put onto there have been mpegs. If you can't do that, then you can go to www.download.com and find the program CinemaForge and download it. This program converts files from one type to another one of your choice, so then you can upload them onto YouTube.