errors when posting a new message

I get these errors each time I post a new message. The post goes through and shows up in my blog but the errors are consistant. Is there soething I have setup wrong?
Thanks.
Paul
http://minichillosconstruction.com/WordPress/

Warning: weblog_ping(/home/minichil/public_html/WordPress/wp-includes/class-IXR.php): failed to open stream: No such file or directory in /home/minichil/public_html/WordPress/wp-includes/functions.php on line 851

Warning: weblog_ping(): Failed opening ‘/home/minichil/public_html/WordPress/wp-includes/class-IXR.php’ for inclusion (include_path=’.:/usr/local/lib/php’) in /home/minichil/public_html/WordPress/wp-includes/functions.php on line 851

Fatal error: Cannot instantiate non-existent class: ixr_client in /home/minichil/public_html/WordPress/wp-includes/functions.php on line 854