Currently Being ModeratedMay 9, 2013 6:15 AM (in response to AppleMan1958)
This solution helped me in the end, but I think there needs to be an update to iMovie to make the gmail address requirement a lot clearer, because at the moment, it only says "username" above the required box.
Currently Being ModeratedSep 24, 2013 1:00 PM (in response to jglar)
Don't forget to change userid to refer to "icloud" instead of "me."
I know this may be old news to some of you, but I was till using my email@example.com for email (it still works) and on many accounts. Biut for some reason Google/YouTube changed my ID for me, and I didn't know. So after much searching and frustration, I tried my firstname.lastname@example.org and it worked.
Hope this helps somebody.