Save and Continue Editing Causes Errors

Hi,

I publish an item, and then go back to edit it – clicking save works fine and updates the item, clicking save and continue editing provides the following errors:

Warning: weblog_ping(/home/jinsan/public_html/wp/wp-includes/class-IXR.php): failed to open stream: No such file or directory in /home/jinsan/public_html/wp/wp-includes/functions.php on line 592

Warning: weblog_ping(): Failed opening ‘/home/jinsan/public_html/wp/wp-includes/class-IXR.php’ for inclusion (include_path=’.:/usr/lib/php:/usr/local/lib/php’) in /home/jinsan/public_html/wp/wp-includes/functions.php on line 592

Fatal error: Cannot instantiate non-existent class: ixr_client in /home/jinsan/public_html/wp/wp-includes/functions.php on line 595

What’s going on here?

I am using the the following release wordpress-2005-02-12

Thanks in advance