If you get Encryption error on login using root then try following.

Login as root in shell/ssh
1. try setting new password for root user.

passwd

if this does not help then try
2. Check hashing (hashing needs to be md5 or )

authconfig --test | grep hashing

if you get following “password hashing algorithm is descrypt” then you need to change hashing type.

authconfig --passalgo=md5 --update

then again set new root password

passwd

Supported Encryptions are:
MD5: "authconfig --passalgo=md5 --update"
SHA-256: "authconfig --passalgo=sha256 --update"
SHA-512: "authconfig --passalgo=sha512 --update"

Note, all users need to change their passwords in order to generate hashes using new encryption.