This is a false warning. Please click "Ignore"
This is a known issue.
Download and install hotfix
Select a simple NTFS partition as a destination.
Stop the nonstop backup first, then you will be able to safely remove the USB disk
This error message can be safely ignored
Make sure that Nonstop Backup service is started
Using True Image 2013 by Acronis Nonstop Backup
This is a known issue