Can't login to MacBook Pro because keystrokes are repeated! Every key I type in the login screen is repeated, so I can't type my correct password! (unfortunately my password is not comprised of pairs of characters)

I recently tried to speed up my key repeat rate via this post but after reverting that change the problem is still happening. It only happens on the main login screen after boot; if I go to switch users the keyboard works normally. Fortunately I've found a workaround through the guest account, but I would really like to know how to get my main login keyboard back to normal! 

Any ideas?
Try looking at the InitialKeyRepeat default for the sudo account. I had the same problem, and noticed this that for my user account defaults read -g InitialKeyRepeat returned a value of 25. But sudo defaults read -g InitialKeyRepeat returned a value of 5, which is much faster. I changed the value for sudo using this command:

sudo defaults write -g InitialKeyRepeat -int 25


and I no longer have a problem typing my password at the logon screen. This page is helpful for more details.