I'm using a Drupal 4.7 on this website and for all my pages it was showing a "page not found" error. The error.log file said
Premature end of script php5.cgi
Switching over the php4 didn't help either, just the error message changed a little:
Premature end of script php.cgi

After disabling some modules in drupal, I found the the
Textile module is the culprit. The Drupal 4.7 version is not maintained anymore and is from nov. 2006. I didn't want to upgrade to Drupal 5.x so I got to find another solution.
A solution is here http://leon.info.tm/en/salvation-textile-drupal-module, but it was to much work for me, the lazy programmer that I am.

So I went to the php.net website and on the PCRE docs I found that starting with PHP 5.2 two new configurations variables appeared: pcre.backtrack_limit and pcre.recursion_limit, both with default "100000".

The solution seemed simple. Open for editing sites/default/settings.php and add these lines:
// fix for textilePHP pcre bugs ini_set('pcre.backtrack_limit', '1000'); ini_set('pcre.recursion_limit', '1000');

The default for this variables are 100,000, which due to bugs in Textile or PCRE consumes all the available process stack and eventually crashes PHP. I guess you were wondering what those "core" files were doing in your site. Those are
"core" dumps of the memory when PHP crashes. You can safely delete them.