And you say even after you dump your Cookies, you are still logged in? That is wierd.

Try naming the cookies that your Forums store in Forums Administration/Configuration to somethign unique. POssibly the cookies from another site with the same named cookie is having an effect, but dumping all your cookies should solve this.
Also try dumping ALL your Internet Temporary files as well.

Just for a goof, if you have another browser, IE, Netscape, whatever, try a different browser as well to see if it is browser related. I don't think it is File related ...at least I have never seen that. :?

mikem