The CBT volume filter driver may enter a state where incrementals are always promoted reporting that "there was an error encountered while loading the CBT Block Driver" in the backup log as the reason for promotion.
Image-level incremental backups persistently promote to full, likely following a major software change, unclean reboot or upgrade of Windows from one release to another (IE: 2012 to 2019).
To resolve this issue, follow the steps below to reinstall the the Unitrends Volume CBT filter driver:
- Log into the affected system
- Uninstall the "Unitrends Volume CBT Driver" using Programs and Features or App & Features.
- Ensure the contents of C:\Unitrendsvcbt have been emptied.
- In certain cases, the a log file cannot be remove; It is okay to ignore this.
- Run uvcbt.msi, which is typically located in C:\PCBP\Installers.
- Complete the wizard.
- Reboot if not prompted by the Wizard.
Note: These steps are specific to image-level backups, not Hyper-V host-level backups.