y tried the sites listed above and y have no problems at all, its kinda funny, y hosted my site (www.viciopolis.tk) on a apple 800mhz 256ram trough a 512 kb connection, and some users, some times, not always get stuck in the login loop, i tried everything in the list, take off firewall, increase the session time, and not to use other software, but i still have two issues,
1.- The login loop, people keep telling me that when they have problems login in at www. they try my ip adress and everithing work fine (strangely just 1 or 2 times it didnt worked too) and.... people from a isp cant post... long post, they can post short post, but, large ones or post with pictures they cant...
any ideas..

well i have the same problem.. i used to have a firewall but i unisntall and the problem continues.. y checked the user.php and all, i turned on all the debugs and nothing... maybe is my user's isp, because sometimes only the ones with the same isp fail to login, but.. is something to do? they tell me they are able to login, no problems, on other XOOPS sites, they have no firewall active.. so i dont know... register is ok, once loged they dont get kicked out, y cleaned the MySQL tables too...

www.viciopolis.tk if anyone wants to check...