If you have a PHP configured with some open_basedir restriction (which is recommended), the WP-Codebox plugin will prevent you from exporting the posts of your blog.

Go to your blog, go in the “wp-content/plugins/wp-codebox” dir and edit the “wp-codebox.php” file :

On line 27, you should have :

include_once "../../../wp-config.php";
include_once "../../../wp-settings.php";

Well, it fails because the plugin doesn’t use the good practices, so it’s pretty easy to fix :

require_once( ABSPATH.'/wp-config.php' );
require_once( ABSPATH.'/wp-settings.php' );

I’d like to thank the developer of this plugin for doing such a great job. It brings the power of geshi (not the latest version by the way) into wordpress.

BTW, why change :
* include_once to require_once : Why should we accept that a file couldn't be included on go on ?
* double quote to simple quote : php reads it faster because it doesn't parse vars ("$" starting words).
* no parenthesis to parenthesis : Well, it's a method isn't it ?