There are a lot of topics around since the lately releases of WordPress that comes with a Fatal error when you don't got enought php memory provided by your hostingsupplier.
I was reading this article for editing the wp-config to set the memory up right: I read the following line:
note that many hosts set the PHP limit at 8MB.
Since i've got the fatal error also i found out that i am provided with 32M of memory and still that isn't enough.
My point, why WordPress become so heavily developed that you can't install it on a light hosting package the most users are supplied with!?