I've had a few separate imports crash with a fatal error in the last month:
Sorry but we are not able to provide this at the moment. DB Error: already exists
Fatal error: Uncaught CRM_Core_Exception: [0: Transaction integrity error: Expected to find active frame thrown in /home/user/public_html/sites/all/modules/civicrm/Civi/Core/Transaction/Manager.php on line 107
In my case it seems to have something to do with external IDs that already exist in the database and are also in the import file. How can I avoid having imports fatally die in the middle of things?