Warning message issue

I continue to get the message:

Warning: require_once(/home/…./blog/wp-includes/class-IXR.php) [function.require-once]: failed to open stream: No such file or directory in /home/…./blog/wp-content/plugins/stats/stats.php on line 421

Fatal error: require_once() [function.require]: Failed opening required ‘/home/…./blog/wp-includes/class-IXR.php’ (include_path=’.:/usr/lib/php:/usr/local/lib/php’) in /home/…./blog/wp-content/plugins/stats/stats.php on line 421

every time I try to activate the WordPress stats plugin even though I’ve removed the file and reloaded it via ftp so I know it’s there. Any ideas? I’d really appreciate the help!