I am new to the forum but have used mint for many years now. Tonight when I tried to do an update the pop up asked for the administrator password. When I tried to type it in the pop up would take several seconds to display each letter (as a dot of course) no matter how slowly I typed the password was not accepted. I using Mint 17.2 and have been since the update came out. This is the first time I've encountered this problem. I tried a reboot but the problem persisted. The keyboard responds normally at all other times. Any help you can offer would be welcome.
Thanks

Welcome to LQ!

Do not know how to fix it, but I'd recommend workaround - use apt-get from command line to update and upgrade your system. Once everything is upgraded your problem may go away.

Just to make sure I understand, have you created a known password for root or are you using sudo with user's password as the sudo and gtksu password?