I tested out your site with the data you sent me in PM and I found the problem.
The reason that things did no longer work after the first click in Phorum is that you had yoursite.com configured in the Phorum HTTP Path setting, while you are accessing your main site and the first page of Phorum through www.yoursite.com.
Because of the hostname difference, cookies were not transferred after the first click in the forums.
If things do work for you, then you probably strart out at the yoursite.com URL instead of www.yoursite.com, making the cookie available over all pages.
I updated you HTTP Path in the forum general settings to fix the cookie issue.
To make things robust, you should add some rewriting rules to you site to always redirect "yoursite.com" to "www.yoursite.com".
Maurice Makaay
Phorum Development Team
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