Did you try visiting that URL? It gives you some tips:
In most cases signing in from the web should resolve the issue, but you may also want to try these troubleshooting tips:
Make sure your mail client isn't set to check for new mail too often. If your mail client checks for new messages more than once every 10 minutes, your client might repeatedly request your username and password.
Try clearing the CAPTCHA (learn more). If you're a Google Apps user, and this doesn't work, you may not be a transitioned Google Apps account user yet. Try https://www.google.com/a/yourdomain.com/UnlockCaptcha instead. Be sure to replace 'yourdomain.com' with your actual domain1 name.
Try changing your password according to our tips on creating a strong password.