Drupal Architect

This error can show up as a blank page, or a page with a header stating zero byte sized reply. Check your logs, and if you find a segmentation fault error, it could be becouse of your opcode cache. The fix is to use APC cache (Alternative PHP Cache) instead of eAccelerator or X-Cache. X-Cache and eAccelerator both have known issues when used as a opcode cache with Drupal under a heavy load.

Why use an opcode cache? Using an opcode cache is an absolute must in a LAMP environment. This cache stores pre-compiled code in memory or on the file system, so that the code does not have to be compiled every time the page is served. This greatly improves page serving speed, and cuts down on CPU load.