One particular complaint reads: Lucky someone seems to have found a workaround until Microsoft offers an official fix for this issue:

Instructions

  1. Open Command Prompt (as administrator) and run the following command:
  2. Delete the datastore.edb file stored in the following path:
  3. Open the Run command and type cleanmgr and the click on Clean up system files. Make sure that windows software updates are selected and perform disk cleanup. This will take a few minutes.
  4. Restart Windows 8.1.
  5. Run Windows Update, all history will be gone but it will detect the firmware update again and this time it will install successfully. Source Microsoft via Neowin All content on this site is provided with no warranties, express or implied. Use any information at your own risk. Always backup of your device and files before making any changes. Privacy policy info.