Thx for your answer Anthony.
We are running a vBulletin 3.5.4 board.
By the way, the error.log i should take a look, where is it located? .. in the admin cp logs there is nothing about psistats (except of the psistats updated message every hour).
The referrals sites statistik in admin cp works.. just the psistats.php which should be pubic to everyone at the moment shows a blank page.
Wanna take a look?
I really have no clue about yet, would be sad if i can't get it working because i like the idea x)