How to Fix Fix Error 0x8007066C — Windows Installer Upgrade Sequence Failure on Windows
Getting Windows error 0x8007066C? Installer upgrade sequence failure? Software update fails during upgrade sequence? MSI upgrade chain broken? Program upgrade process rejected? Fix error code 0x8007066C.
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Main Troubleshooting Guide
How to Fix Microsoft Store Not Working →Complete symptoms, causes, and step-by-step solutions
Symptoms
You might be experiencing this problem if you notice:
- •Software upgrade fails with error 0x8007066C
- •MSI installer reports upgrade sequence failure
- •Program updates abort during upgrade phase
- •Windows components fail upgrade chain validation
- •Feature update reports installer sequence error
- •Repair install fails with upgrade sequence rejection
Common Causes
- ⚠Previous version registry entries corrupted
- ⚠Upgrade sequence table in MSI database damaged
- ⚠Multiple versions of same software causing conflict
- ⚠Windows Installer cache missing required transform files
- ⚠Incomplete uninstall of previous version blocking upgrade
- ⚠Group Policy Software Installation interfering
Solutions
Solution 1: Clean Previous Version and Reinstall
- 1Uninstall current version completely:
- 2Settings → Apps → Installed apps → find the app → Uninstall
- 3If normal uninstall fails, use the installer:
- 4Run the original installer → choose Repair or Remove
- 5Clean leftover files:
- 6Delete folders in C:\Program Files for the app
- 7Delete folders in C:\ProgramData for the app
- 8Restart PC
- 9Install the new version fresh
Solution 2: Fix Windows Installer Cache
- 1Re-register installer components:
- 2CMD as Admin:
- 3msiexec /unregister
- 4msiexec /regserver
- 5Check installer cache:
- 6C:\Windows\Installer should not be empty
- 7If files are missing, run:
- 8sfc /scannow
- 9DISM /Online /Cleanup-Image /RestoreHealth
- 10Use Microsoft Program Install and Uninstall troubleshooter
- 11Download from support.microsoft.com
- 12Run and let it detect and fix installer issues
Solution 3: Registry Cleanup for Upgrade Path
- 1Open Registry Editor: Win+R → regedit
- 2Navigate to:
- 3HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall
- 4Find entries for the affected software
- 5Note any entries showing old version numbers
- 6Export the key as backup before changes
- 7Delete orphaned entries for old versions
- 8Also check: HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node (for 32-bit apps)
- 9Restart PC and retry installation
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