Fatal Error : Call to undefined function simplexml_load_file()

I am using PHP version 5.2.1. I am getting the following error.
Fatal error: Call to undefined function: simplexml_load_file() in E:\domains\****\wwwroot\wp-content\plugins\view.php on line 645.

Can anyone explain me about this error and how do I solve this.....

In php 5 version, simplexml_load_file is enabled by default. I would suggest you to please contact your host and find out why simplexml_load_file is not supported on your server.

Check whether simplexml is loaded by looking through phpinfo()

I also got the same Fatal error: Call to undefined function: simplexml_load_file() on line number 124 in my php script. The thumbnails were displaying fine but when I click on it, I got this error...