When migrating or accessing Google Gmail, you may encounter one of the following errors even though your user name and password are correct: 1) Web Login Required or 2) Invalid Credentials.
Like the big black box Google is, they don’t comment on security related problems/features that they implement. In addition, the error codes/messages that they present are not always decipherable. When searching the internet for these errors, you will only read about user experiences and what people have tried.
Because of the large amount of mailboxes that we migrate from Google Apps/Gmail to Microsoft Exchange, we are very familiar with these errors. You will encounter these messages upon authentication if your account “looks” to be compromised. Google detects this based on IP address access to your account and other mechanisms that they won’t divulge to the public. With our now “always connected” world, it’s very easy to “look” compromised because we are connecting from multiple devices all the time, whether it’s your desktop, mobile, kiosk, friend’s house, etc. IP addresses can be mapped back to physical locations but there is a chance that there is a false positive.
If you encounter these error messages, you can unlock your account for access by performing a CAPTCHA with Google.
If you are accessing a regular account (your email address ends in @gmail.com), you can unlock your account by following the instructions at https://www.google.com/accounts/DisplayUnlockCaptcha
If you are accessing a premiere/enterprise account (your email address ends in your own custom domain), you can unlock your account by following the instructions at https://www.google.com/a/domain.com/UnlockCaptcha where domain.com is your own domain.