If you login to PP and you are recognized in UBBThreads then the reverse should in theory work as well since they share the same cookies.
Try deleting all the cookies from your machine and login from fresh. This might just do the trick... I know that PP uses for sure the w3t_myid section of the cookie to check authentication.
What you can also try is:
Clean up all your cookies.
Log in to your threads.
Open the folder that cookies are stored and take a copy of your cookie (should be [username]@www.esportbike.com (where username is the user name you are logged in the machine you are accessing the site).
Open it in Wordpad or other text editor.
Log out and delete all the cookies again.
Log into PP and check the cookie again.
Copy it somewhere else and open it again in Wordpad
The differences should not be huge between them. The basic information should be the first two lines. For instance in my case here in TDev is:
w3t_myid
10000
www.ubbdev.com/which means that I am the user with U_Number 10000 and I am logged into the
www.ubbdev.com domain.
Maybe this will give you some more hints on what is going wrong.
Warm regards
Nikos