one of the links in that thread is wrong.

should be: http://www.powertoolsforum.com/modules/xoopsfaq/index.php?cat_id=2q5q5

This one explains how your users should set there firewall

I think there also is a way to change the http referrer code in XOOPS somewhere,

Xoops has increased security, I understand that 90% of the logins problems are related to bad settings in the user firewalls

Edit: developers dont recomend this but a way or hack Here

edit: need to find out which versions are causing this, looks like older versions from the posts?