This article describes how to install and use the XEN Hypervisor on Fedora Linux 8. I use Fedora Linux as host operating system (Domain 0) and I use Fedora as operating system for the paravirtualized  [ ... ]

Solution: make sure that session_start() is the first statement in your PHP script. Even a  white space or or any other characters before session_start() or even before <?PHP tag will result in an [ ... ]