Fatal Error upgrading to 2.3.3

Hi there, this is my first post here. I had been able to install an older version of wordpress and had lots of nice plugins and resolved most of my problems on my own. I let the site inactive for a bit and now I’m back and just tried to updated it to 2.3.3

I get the following error. I did copy the contents of content (as well as themes and plugins manually) as said.

Error is:
Fatal error: Cannot redeclare get_lastpostdate() (previously declared in /home/daunda/public_html/wp-includes/functions.php:111) in /home/daunda/public_html/wp-includes/post.php on line 1684

I get that error in /upgrade.php

Website is: http://aerochile.forcehosting.cl/

Any help would be greatly appreciated. Thanks!