The error happens when php is run through fastCGI, and it is related to this problem that's reported on php bugs: http://bugs.php.net/bug.php?id=36705
To duplicate the problem, you need to compile php sapi/cli with fastcgi support, and run it under apache2/mod_fastcgi. This is what an entry in the error log looks like:
[Sat Apr 01 23:30:20 2006] [error] [client 66.215.220.80] FastCGI: comm with server "/var/www/fcgi-php/php" aborted: error parsing headers: duplicate header 'Status'
The relevant section of code is in wp-includes/functions.php
@header("Status: $header $text");
@header("HTTP/1.1 $header $text");
According to the suggestions on the php bug list, one workaround would be to rewrite this section of functions.php as follows:
if (substr(php_sapi_name(), 0, 3) == 'cgi')
@header("Status: $header $text");
else
@header("HTTP/1.1 $header $text");
I made this change myself, and it seems to make wordpress work both under mod_php and mod_fastcgi. I'm running apache 2.0.55/php 4.2.2 I've tested this code myself in both mod_cgi and mod_fastcgi configurations and it seems that all is well with it. I haven't tested this with php5, apache 1.3.x, or the extremely new apache versions above 2.0.
