Hi guys - I'm on the YouTube team. Apologies to hear about some of the login difficulties you've been having in iMovie. It's due to a change in our login process that we made late last year / earlier this year.
*The change we made*:
If you've linked your YouTube account to a Google Account, you now need to sign in with the password from your Google Account. Once linked, your old YouTube account's password is no longer accepted. There are a few different reasons we made this change - most notably, account security.
*The solution*:
*Option 1)* You can successfully sign in by putting your Google Account's password in the "Password" field, instead of your old YouTube account's password. Or, if it makes it easier, just sign in entirely with the Google Account linked to your YouTube username (i.e. the Google Account's email address + your Google Account's password).
*Option 2)* As others have pointed out, you can unlink your accounts (at
http://www.youtube.com/myaccountunlink). But eventually all YouTube accounts will be required to be linked to a Google Account (reasoning here:
http://youtube-global.blogspot.com/2010/07/connecting-google-account-to-your-old er.html), so I humbly recommend option 1 to save yourself annoyance down the line. 🙂
(YouTube accounts created after May 2009 shouldn't have this problem, by the way - just older ones that are now linked to Google Accounts.)
The "use your YouTube username@gmail.com" suggestion from earlier in this thread doesn't really work, by the way, unless your Google Account happens to a) use a Gmail account as its email address, and b) share the same username as your YouTube username.
And I hope we can work with the iMovie team soon to help make the login process aware of this particular error (so it can guide users to the solution).
Hope that helps.