The backup tool in SugarCRM does not work at all when in a shared server environment.
I have a better way to backup your SugarCRM that works. To restore your SugarCRM you need to restore the database first and then restore your SugarCRM files. Here is how it works:
First you need to export your full database. (I use MySQL) You do this from PhpMyAdmin. In order to reach it you have to log in your Cpanel, go to MySql databases and click on the link to PhpMyAdmin.