If you are using an iOS device (iPad or iPhone) you might find that you are unable to log in with a new Google account. This is usually because there are already too many Google users logged in on that device.
You can usually fix this by simply logging out some of the other accounts. Don't worry - nothing bad will happen to the other users' accounts and they will be able to log in again later.
To log out of Google accounts, open Safari on your iOS device, and go to: https://accounts.google.com/Logout
Log out at least one account, then try logging in again yourself.