Im confused why an insert in the related categories table would have a reviewer IP column.. It's 2:30 am here now so I'm afraid I'll have to leave it at that for now...

If you'd care to, send me a reminder message via the compose link under Dew-Code Mailbox to the left, addressed to Dewed of course. Show me the URL of your installation and I'll shed what light I can.

And to be honest, sessions aren't really necessary for the script at all, although PHPLinks has session support, It doesn't actually use them for any purpose that I could see. Click fraud etc is handled differently.