Theme blogs MU don't work

i install the Blogs MU theme on my websit and got the following error:
"Fatal error: Call to undefined function wp_get_theme() in /hermes/bosweb/web174/b1744/ipg.manuelescobar79/compiteweb/wp-content/themes/blogs-mu/_inc/functions/options-functions.php on line 10".

And now my websit is no longer visible. Can you say me how i make the theme work