Error message after installing WP 2.5.1

Hey there,

I just installed / upgraded my old 2.3 version to 2.5.1., and since then get an error message on mu site:
Fatal error: Call to undefined function: get_shortcode_regex() in /www/htdocs/w008f9a0/wp-includes/formatting.php on line 95

I changed the wp-admin and wp-includes folder on my ftp, as recommended on wordpress for upgrading.

but since then i can’t see any of my content on the site anymore. since i’m not that firm in installation and html etc., i appreciate a lot if soemone can give me a hint how to solve this problem…

thanks,
mohak