After changing a username in the Admin Panel of erwin Mart Administrator, the following warning message appears:
"Modifying the username will close all existing sessions and reset password for the user. Continuing with the operation may result in the loss of data for a connected user.
Do you want to continue?"
If you choose Yes you will get an "Access Denied. Login to continue." error message and you are signed out.
You will not be able to sign in using your new username and existing password.
This is as expected. When you change a username in the Mart Administrator, the password reverts to the default password, which is "Erwin123", so your new credentials will be your new username that you set with the default password of "Erwin123". You can and should change this default password.