BuddyPress.org

I clicked on “update” for the new buddypress plugin (1.5.7 I think) and the update page said the update was successful but then it had a fatal error below it. I hit “refresh” on my browser and now my site won’t load and I get the same fatal error saying:
“Fatal error: Call to undefined function is_site_admin() in /home/rebsen1/recreationtherapynetwork.com/wp-content/plugins/buddypress-links/bp-links-core.php on line 704”

My site is http://www.recreationtherapynetwork.com.

Please help me!!!