My X Server become ZOMBIE

[Alessandro Torrisi <alessandro torrisi eurone it>]

Well I've got a problem with X, I was setting up my xscreensaver when all the 
X system locked up ! I connected with my notebook with SSH and there was a X 
process with a 90% cpu and 0% memory .consumption. 
The process was Zombie. I had to reboot my server. Do you know why ?? 
What is happening ? I had this problem also with FC2 !

Bye, Alex