Upgrade to 2.5.1 security files problems

I’ve just upgraded the three 2.5.1 files suggested to fix security issues (admin.php x2 and pluggable.php).

I now get the following error when trying to login:

Fatal error: Cannot redeclare media_upload_tabs() (previously declared in /var/www/my-site.com/wp-includes/media.php:5) in /var/www/my-site.com/wp-admin/includes/media.php on line 11

Is there anything I can do? Or, should I revert to the original 2.5 files?

Thank you.