Warning: Use of undefined constant user_level - assumed 'user_level' (this will throw an Error in a future version of PHP) in /homepages/3/d98111892/htdocs/insanelabs/htdocs/wp-content/plugins/ultimate-google-analytics/ultimate_ga.php on line 524

Run:

apt-get install debian-keyring debian-archive-keyring
apt-key update

and try again.