My guess is that your password(s) are too short to meet the required minimum password length. See min password length and min admin password length in site settings.
You’re saying that after you upgraded you were unable to login using your password?
Did you try resetting your password?
Does it affect only admin passwords? Is your admin password shorter that the required length for logins? If this also affects normal users, are those user passwords too short for the required password length requirements?
What version were you running before?