I’m the biggest Google fan in the world but I’m writing about this because it confuses/frustrates me all the time. The Google Apps database is a entirely separate entity then the Google user database. So firstname.lastname@example.org e-mail address and password will not work when trying to do anything with Google that isn’t your Google Apps account.
The solution is to simply register your Google Apps e-mail with Google and use the same username and password. I completely understand why the two are desperate but it’s difficult to remember to change the password in both places.
When i refer to your Google account this is the e-mail address and password you’ll enter when you log into anything Google owns such as youtube and anything else they have acquired.