404 header breaks loading 404 template

Hello,

I got the following problem (only on my online server):
My 404.php template is not loaded by WP during an unknown page/post request.

Online server is running:
– PHP Version 5.3.3-7+squeeze3
– Apache/2.2.16 (Debian)

After some debugging I tackled down the occurrence of the problem:
During the request WP sets the header to 404 in the following file ‘wp-includes/functions.php’ with function ‘status_header( 404 )’.

The ‘status_header’ functions calls the PHP ‘header’ function which results in a “404 Not Found” page where it should load the ‘404.php’ template.

I guess this is a server related problem. Anybody some ideas?

thanks in advance!