It has come to our attention that recently many users have been unable to log into the site even after resetting their passwords. It appears to be a cookie issue and seemingly is more prone with the latest version of Firefox.
I would suggest trying to following and that should help narrow down the problem or even fix it. Once you are in, you can usually switch right back to your normal browser without issue as long as you clear the cookies.
1. Try a different web browser. Ie (Google Chrome, Mozilla Firefox, Opera, Safari) and see if you are able to log in with the password you received in your email with a different browser.
2. Reset your cookies. This differs from browser to browser, but please delete ALL your cookies and then try logging into the site.
For Firefox, this link helps: Can't login? Reset password and still not working? Check here! - Nexus One Forum - Google Phone Forum
If you are, proceed to step 3.
2. Now that we know the password and account work, try clearing all your cookies in your existing browser and then logging in. Sometimes cookies get corrupt and they prevent you from logging in, and this is an easy fix so you can continue to use your favorite browser.