Welcome to Android Central! If this is your phone and it's not accepting the password you created (or if it's asking for a password you never created), then the update might be buggy -- this has happened on other phones before, and unfortunately the only solution is usually to do a factory reset. This will of course wipe all the data off your phone, so hopefully you were keeping the important data backed up or synced on a regular basis.
Has this always been your phone, or did you get it from someone else? If the latter, then it's probably asking for the password the other person created.