the AIX command to create a new user is mkuser, but if you are asking, then I suggest to not try but to use the gui/txt administration interface: smitty ( txt ) /smit ( X11 ) by typing the shortcut ...
First off, i am glad you could resolve your issue. But: a reboot is (most times) not the way to resolve things. After all, we are not on Windows - we use a real OS with real error-correcting...