I am not referring to the classifieds. You can do that after you install and can login to our admin panel under cookie settings.
I am quite sure if you login here you can gain access to your admin panel Login - PhotoPost Classifieds
The issue is as I figure it is your cookie path in your forum is probally not / which it needs to be or your domain name changes when you go to classifieds say www or no www
That means as far as cookies are concerned two different domains that is why cookies must be set between both applications like we state in the FAQ. Cookies and Login Problems!!
If your cookies are not aligned between the products you will not have a uniform login.