On a certain forum I got banned on for just replying sternly to someone, no bad language or nothing... Anyway, I created a new account and it said i don't have permission to post. How do they know its me hehe. I thought I had a dynamic ip, one that changes alot, so how could they know its me. For fun I used another computer here at home and blam, they got that one to. Very interesting. I still love DP the best!
If the forum is running Vbulletin, they might have something like this Multiple account login detector (AE Detector) installed. http://www.vbulletin.org/forum/showthread.php?t=125871 What ever computer you logged into the site with, it got a Multiple account cookie put on it. This is totally separate from your log in cookie. When you log in as a different user, the site checks for the Multiple account cookie. If the cookie exist, the admin of the site gets a PM with your details, username, account and other things. If the site has that modification installed, you need to clear the cookies on every computer you used to access the site with. The cookie does not expire for years, so you have to clear it manually. I can not say for sure that is the "exact" mod that is catching you. The site owner might have a custom made modification. But most of those multiple account login detector programs are cookie based. I know about this modification and how it works because I have it installed on my site. It has come in real handy keeping trouble makers out. I caught one guy I banned about 3 months earlier after he created another account.