Problems with WordPress 2.7

Hi,

I just upgraded to WordPress 2.7 but when I try to install plugins or update themes, I get the following message:

Fatal error: Cannot redeclare pclziputilpathreduction() (previously declared in /home/username/public_html/wp-content/plugins/wordpress-automatic-upgrade/lib/pclzip.lib.php:5421) in /home/username/public_html/wp-admin/includes/class-pclzip.php on line 5498.

(I replaced actual username with “username”)

Can anyone help?

If there is no solution, how do i get back my old version of WordPress from my backup files?

Grateful for help.