I noticed this Ticket regarding the requirement that AdminTools needs PHP 5.3 and the user assumes that his host only offers PHP 5.2.4
https://www.akeebabackup.com/support/admin-tools/16451-php-version-2.html
Keep in mind that there are often methods of "upgrading" to Php 5.3. Usually a call to your hosting's tech support, or a check of your host's faq will show you how to add a line to your htaccess file or uploading a special .htacess file to below your root will provide the PHp 5.3 you need for AdminTools.
...Rowby