Acronis Backup 12.5: "This machine cannot be selected directly" warning in Linux-based bootable media

Symptoms

1. You boot a machine with Acronis Backup Linux-based bootable media
2. You start a backup wizard, click on Items to backup and select the entire machine

3. The following warning appears:

   This machine cannot be selected directly.
   A previous agent version is installed on the machine.
   Use policy rules to select this machine for backup.