404 error after login

I have been successfully logged in to my site and made changes and updates.
The next time I logged in I get a 404 error (/login/authenticate/concrete not found). Any solutions to resolves this please? I notice I don’t have an htaccess file in the root.

What changes did you make? It sounds like you may have changed the view permissions on a dashboard page or something. Logging in as the admin user should probably work though.