Drupal 6.15 Page Cache crash

Hello Everyone,

I have a site using:

Drupal 6.15
MySQL database 5.1.40
PHP 5.2.11
Web Server: Apache/2.2.14 (Unix) mod_ssl/2.2.14 OpenSSL/0.9.7a mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635

Ever since updating the site to 6.15 from 6.14 the site crashes when Page Cache (Normal) is enabled. The pages load at random but usually give a Server Error page without a code. It looks as if the page doesn't exist then randomly it will work. The crash happens on different browsers on different computers in different networks.

I have Page Cache disabled now because the site is a popular school website and needs to be online. Anyone have any ideas of where to start?

Thank you kindly in advance!