You must sure your server is configured for  PHP 5.2 or upper.
To know the php version on your server you can create a page "test.php" inserting between the tags < body > < / body >  the following php command:

<?php
phpinfo();
?>

This page must load in the principal root of your domine and in your browser to type  "http://yourdominename/test.php."
If php is not the 5.2 or upper,  contact the technical support of your hosting to know the PHP versions they have. If PHP 5.2 or upper is avaible ask to configure your server space or to send to you the parameters to configure your server space. If your hosting is a good and serious hosting, usually these information about configure your server space from PHP4.x to PHP 5.x 5.0, you can find them on their on-line help and guides.

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