PHP: error when requiring PEAR.php

Question

I'm having an include path problem:

get_include_path() returns .:/usr/share/php:/usr/share/pear

Pear.php is in /usr/share/php:

# ls /usr/share/php
Pear.php

but require 'Pear.php' gives me a server error! What's going on?

Update: I got around the issue by using Apache's php module instead of suExec and cgi. I still don't know what exactly caused it, though.