Changing admin login name in wordpress multisite

Hi I followed the step by step tutorial as outlined in here: https://premium.wpmudev.org/blog/change-admin-username/
I did all the steps as required, but I am unable to login with my new username. I used 17 characters and I included many different characters and numbers. Could you please guide me to why I am unable to login with my new username? I use the itheme sercurity plugin, can that has something to do with it.
Thank you,
Inger