Unitrends Volume CBT Driver Reinstallation (Image-Level/Block Agent)


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:

  1. Log into the affected system
  2. Uninstall the "Unitrends Volume CBT Driver" using Programs and Features or App & Features.
  3. Reboot
  4. 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.
  5. Run uvcbt.msi, which is typically located in C:\PCBP\Installers.
  6. Complete the wizard. 
  7. Reboot if not prompted by the Wizard.

Note: These steps are specific to image-level backups, not Hyper-V host-level backups.

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