Some users are experiencing troubles after upgrading to 3.7. The problem is that WordPress deletes one of our files when upgrading and we are checking with them why this might happen as we are not in control of this.
For the Ai1ec_File_Not_Found exception the solution is to copy one file which is deleted when wordpress upgrades. Look here http://wordpress.org/support/topic/not-compatible-with-wp-37?replies=8
Another solution is to upgrade to 1.10.1 standard which can be downloaded from time.ly performing a manual upgrade http://support.time.ly/manually-upgrading-the-calendar/ - REMEMBER TO FOLLOW POINT 2 OR YOU WILL LOSE YOUR EVENTS - Sorry for shouting but we get complaints that all events are lost from people who do not follow point 2.