[phpOpenTracker-general] page impressions equals visitors

hi,

I'm trying to downgrade phpopentracker to run with php 4.0.6.

therefore I have changed all prefined variables like $_SERVER into their
predecessors
and made sure they are in the current method scope ('global...').
(everthing tried with version 1.50rc1)
It works fine, except for page impressions equals visitors.
I tried the original release on php 4.3.1 und got the same.

does anyone have a clue?
maybe I am doing wrong something here.

regards,

stefan