"WordPress uses a program wp-cron.php which is called when a certain amount of time has passed.

"Every time your blog is accessed by a user WordPress checks if the time is there to call wp-cron.php by comparing the time wp-cron.php last ran and the current time and when it determines it needs to run wp-cron.php it does so.

"The way wp-cron.php is called is by the PHP fsockopen and doing a HTTP call. One of the parameters is your site’s URL. The fsockopen function needs to resolve that name to an IP address, that’s just the basics of the internet.

"I guess you see the problem now, the function runs on the server and tries to resolve it’s own name. Which in this case doesn’t work."
Read More : Linux Today