ssh-authtication

Hi folks, umm, I have a small problem. When setting up our server, I tried to get the best security as possible. Maybe I changed some config-file to fit our needs to allow ssh-logins only from specified users.(But I have no idea which file this was :-(( ) Now I want to allow another user to login using ssh. I made ssh-keygen for this user, entered the password, copied identity.pub to authorized_keys in the .ssh-directory. But when trying to login via ssh, servers sends permission denied. What else must be done ? TIA ---Stephan