A failing login can have several causes. Maybe you have a typo, changed your password recently or another problem is causing the login to fail.
You have a typo or some keys of your keyboard are broken.
Caps lock (the key above the shift key that causes all typed letters to be in CAPITAL case) is active. Your password is case sensitive.
You changed your password recently. The incorrect password is still saved in your browser.
You are entering an incorrect email address and/or password.
Corrupted cookies may sometimes cause problems during login.