Hi!
I logged in to the admin-panel with the default admin/admin l/p.
Then I decided to change the username and password.
When I tried to enter the admin-panel after that, it wouldn't open and it resulted in a 404 after a while.
I solved it by setting admin/admin, entering admin-panel, log out, then change username/password and log in again.
It should give the login-form instead og ending up in 404...