An attempt was made to login to a blocked account. The server prevents unauthorized account access by detecting suspicious login attempts. For example, an account typically becomes blocked after too many attempts to login with the incorrect password. To unblock an account that you access programmatically, you'll need to manually go to the following URL in a browser:
http://www.google.com/accounts/displayunlockcaptcha



Sounds like attempts were made to login to your account and they were wrong so the server blocked the account from being accessed...

Any more questions about Gmail, you should post them here: Google Groups