You can navigate to this report by logging into your Connect 5 dashboard and navigating to 
  1. Recipients
  2. Contacts
  3. Import Data
  4. View Import History
Once you land on this screen, you can hover your cursor just to the left of the import and click to expand details.  This view will show you the number of users that caused an error or were imported.  Clicking on that number will bring up which users as well as the error.  

It is important to note, these reports are only stored for 6 days.