error after a restore

hello,

the 2.1 version of didn’t work like i expected so i restored my wordpress directory (wp) and restored the database, but now i get an error saying :

Fatal error: Call to undefined function: language_attributes() in /hsphere/local/home/clogwogn/clogwog.net/wp/wp-content/themes/default/header.php on line 2

in what direction should i look for a solution ?

it’s a 1 on 1 backup of the wordpress directory that was working a few hours ago, so i don’t understand why it won’t work.

any ideas more than welcome!!

best regards,
tom