skrueger03 on "Installed 3.8 and site is broken now"

Upgraded manually to Wordpress 3.8 on http://www.smart-ins.com and got the following error after upgrade.

NOTE: I usually do the upgrade through the dashboard on other sites but for this client it doesn't work with their small-town hosting provider so I have to do it manually. I don't know if that has anything to do with the new error. Everything was working fine until upgrading to 3.8.

Fatal error: Call to undefined function wp_get_current_user() in /mnt/nfs/www/www.smart-ins.com/wp-includes/capabilities.php on line 1342

Here is the code from that file.

function author_can( $post, $capability ) {
if ( !$post = get_post($post) )
return false;

$author = get_userdata( $post->post_author );

if ( ! $author )
return false;

$args = array_slice( func_get_args(), 2 );
$args = array_merge( array( $capability ), $args );

return call_user_func_array( array( $author, 'has_cap' ), $args );
}

I tried reverting back to 3.7.1, but that just returned the same error but this time on line 1286. So, I'm reinstalling 3.8.

Anyone have any ideas? I'm a novice at Wordpress so please use as plain of language as you can. I'd really appreciate some help.