Upgrade errors

Hi,

I am trying to upgrade to WordPress 4.1.1, but I keep getting the following error: Fatal error: Cannot redeclare PclZipUtilPathReduction() (previously declared in /home/phillyki/public_html/wordpress/wp-content/plugins/ready-backup/modules/backup/classes/pclzip.lib.php:5396) in /home/phillyki/public_html/wordpress/wp-admin/includes/class-pclzip.php on line 5452

I actually get this error when I try to upgrade anything. What can I do?