I attempted several times to publish a movie to YouTube, but nothing shows up on my YouTube channel. I went to the troubleshooting forum on YouTube, where it was suggested I try three times. When that wasn't successful, it was then suggested that I export the files outside of iMovie, then try to publish it manually using a YouTube publishing resource. I found that when I exported it out of iMovie, it was in the m4v format. YouTube doesn't support m4v.
YouTube supports my m4v with no issues. Most likely you have an issue with your youtube password. At some point recently, they switched over from using YouTube passwords to linking it with your Google password.