Early today I could no longer login to my Gmail account from my iPhone. The error said something about a wrong username or password. I tried logging in from the iPhone web browser and it worked so the problem was with the Email application.
So what did I do? I used Google’s own power to defeat it 😀
I googled for “iphone gmail login failure” and found the solution. You will have to use your iPhone’s web browser and go to https://www.google.com/accounts/DisplayUnlockCaptcha. There you will have to enter your Gmail email address and password and a captcha. This automagically fixes the login problem.
I hope that helps.