I seem to remember that when I updated one of my boxes from 4.1.2 to 5.1.2b4 I had a similar problem. I think the php scripts in the v5 software are limited to getting files from their own folder only and can no longer wander about the system gathering data.
Maybe the people who have it working are running the phpSysInfo script from within the primary html folder which has special access. Just a thought.
I think there was a fix, but I never bothered trying it.
Try checking the archive for phpsysinfo problem.
Bill.