Hi,
It could indeed be that simple...especially if you just did a vanilla install and didn't tweak anything.
Otherwise, the main config file is /etc/ftpaccess and you need to check what type of users you have allowed. You should have something like :
class all real,guest *
(users with linux accounts are 'real' users)
Also, remember that none of the accounts listed in /etc/ftpaccess can logon to wuftpd and there may also be restrictions in /etc/ftphosts .
Another place that there could be restrictions is the xinetd config file - /etc/xinetd.d/wu-ftpd . Look for entries like 'only_from = localhost' or suchlike.
Apart from the simple tcp wrappers possibility (hosts.allow vs hosts.deny as above) the only other thing I can think of is some error with the FTP pam config ...
For more info on the 530 error you should look in the system log. For example after an error occurs do :
tail /var/log/messages
Hope this helps