Just in case you do not know how to clear your cookies:
In
Firefox, choose Tools, Options in the menu, and click Privacy. You get this screen (this screenshot with the button Show Cookies clicked):

Now either click Clear now (bottom right), that will clear all cookies, or click on Show Cookies, and remove the SANParks ones only.
In
Internet Explorer, click Tools, Internet Options, and in the middle you'll have a button Delete Cookies.
On the main page of the forums there is a link called Delete all board cookies (just above who's online), but that seems not to work perfectly.