Our site crashes when we activate Ultimate Facebook

Hi. We have tried this plugin, but there seems to be some software conflict and the site goes down after its installation...so we have had to disable it. This is the error message we get:
Notice: Undefined index: key in /home/.../wp-content /plugins/post-indexer/post-indexer.php on line 41

Notice: wp_register_script was called incorrectly. Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or inti hooks. Please see Debugging in WordPress for more information. (This message was added in version 3.3) in /home/.../wp-includes/functions.php on line 2758

Pls help!

Tks.