On my installed instance of FUDforum I've enabled user aliases.
Every time I try to set, as administrator, an initial alias for a user the action give rise an error:
404 Not Found
The requested URL [...]/index.phpadm/admuser.php was not found on this server.
It seems that if an administrator modifies the profile of another user the control is redirected to a wrong formed path for the script admuser.php (or something similar).
This not occour when a user (normal or administrator) modifies his own profile.