[Koha] Need help in login to Koha

[aaruswartz at tuta.io]

Dear Team Koha,
Thanks for accepting my request to join the mail-list.

Our office library uses Koha for a long time now.
Librarian has forgotten the user name and password.
I am the System Admin and have reset the Koha admin user password in the /etc/koha/sites/library/koha-conf.xml and in MySQL. I am able to login to the database via both PHPMyAdmin and MySQL CLI.
But unable to login to the Koha site at  http://IPaddress:8000 <http://IPaddress:8000>. 

The login page displays this below message.
"Error: Invalid username or password" message is being displayed. "

OS :  Debian GNU/Linux 8.11 (jessie)
Koha : koha 18.11.03
MySQL: mysql 5.5.62
PHPmyadmin : phpmyadmin 4:4.2.12

Please let me know what is causing the problem and if any fix. 
Thank you.

Aaru_Swartz