installing latest version

Hi,

I tried to upgrade to the latest version of WordPress.
The front end seems fine, but when I try to log in I get the following error:

Fatal error: Cannot redeclare validate_file() (previously declared in /hsphere/local/home/hokstam/sxm-airport.com/media/wp-includes/functions.php:3068) in /hsphere/local/home/hokstam/sxm-airport.com/media/wp-admin/includes/file.php on line 45

What did I do wrong??

Thanks!