hma66 on "Upgrading to 3.3 version"

Hello There,

I got the following message while trying to upgrade wp 3.3 automatically.

Fatal error: Cannot redeclare class Plugin_Upgrader in /home/advert/public_html/wp-admin/includes/class-wp-upgrader.php on line 594

Any solution to the problem?

Thanks in advance.

Best Regards,