HERE IS THE FIX for scheduled backups being stuck on "Preparing file list."
1. From the IDrive application, select "Scheduler".
Select "View and manage all scheduled jobs" from the bottom right-hand corner of the application screen.
2. If you have more than one schedule, remove any that do not match the schedule from the previous screen. This was the problem on my client's computer and is likely your problem too. If you only have one schedule listed, delete it and create a new schedule on the previous screen. My client had two schedules, one that was the current schedule and another that was obsolete.
NOTES:
My client had been suffering from missed backups for the last several months. When I opened the IDrive application on his PC, it would display "Preparing file list" until I manually canceled the backup. There would be at least two other backups in the queue displaying "Preparing file list," so I would have to cancel those as well.