Could you please point out the problem with my nginx config?

Hi,

I've installed new PunBB 1.4.1 with nginx 1.1.13, php-fpm 5.4.0 RC5, and SQlite 3. The setting is simple, my forum runs with Antispam System and JS Quote post extensions.

The problem is: can't register new user because this

Warning! The following errors must be corrected before you can register:

    * A new user was registered with the same IP address as you within the last hour. To prevent registration flooding, at least an hour has to pass between registrations from the same IP. Sorry for the inconvenience.

I've tried with many different usernames, email addresses, and IP addresses (I've used ADSL service to get dynamic IP address) but this error still appears.

Hope you guys could have solution for this one.
Thanks,

Edit: I'm running a reverse proxy for my servers, so this kind of error should be related to the reverse proxy. Nginx log looks like:

10.0.0.1 - - [19/Jan/2012:10:49:18 +0700] "POST /forum/register.php?action=register HTTP/1.1" 200 2576 "http://domain.com/forum/register.php" "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.12) Gecko/20101026 Firefox/3.6.12" "113.x.x.x"

Where 10.0.0.1 is my reverse proxy, and 113.x.x.x is user's public IP address. Did PunBB detect the reverse proxy IP address as the user address?