How to Fix Fix Error 0x80070666 — Another Instance of Installer Already Running on Windows
Getting error 0x80070666 when installing software? Another version already installed? Installer detects existing instance? Can't upgrade or reinstall application? MSI installer version conflict? Fix this installer instance conflict error.
Symptoms
You might be experiencing this problem if you notice:
- •Installation fails with error 0x80070666
- •Error message says another version is already installed
- •Can't install newer version over existing one
- •Uninstall fails too — creating a deadlock
- •Programs and Features shows the old version but Remove fails
- •Visual C++ Redistributable commonly triggers this error
Common Causes
- ⚠Previous version installed and blocking upgrade path
- ⚠Incomplete previous uninstall left registry artifacts
- ⚠MSI product code conflict between versions
- ⚠Windows Installer cache missing repair files
- ⚠Corrupted uninstall information in registry
- ⚠Side-by-side (SxS) version of same component installed
Solutions
Solution 1: Uninstall Previous Version First
- 1Try normal uninstall first:
- 2Settings → Apps → Installed apps
- 3Find the application → click ⋯ → Uninstall
- 4If uninstall fails:
- 5Try Control Panel → Programs and Features instead
- 6Right-click → Uninstall
- 7If that also fails:
- 8Download Microsoft Program Install/Uninstall Troubleshooter:
- 9aka.ms/diag_piu (official Microsoft tool)
- 10Run it → choose the stuck application → Remove
- 11This cleans up MSI registration without needing installer files
- 12After removal: retry your installation
Solution 2: Fix Visual C++ Redistributable Conflicts
- 1This error is very common with Visual C++ Redistributable:
- 2Open Settings → Apps → Installed apps
- 3Search for "Visual C++"
- 4Note all installed versions (2005, 2008, 2010, 2012, 2013, 2015-2022)
- 5Each year can have x86 and x64 versions — this is normal
- 6To fix: uninstall the SPECIFIC version that matches your installer
- 7Don't uninstall all of them — other software depends on them
- 8Then reinstall the version you need
- 9Download latest from: learn.microsoft.com/en-us/cpp/windows/latest-supported-vc-redist
- 10If multiple versions conflict:
- 11Uninstall all 2015-2022 versions (they're unified)
- 12Install the latest "Microsoft Visual C++ 2015-2022 Redistributable"
- 13This covers all versions from 2015 through 2022
Solution 3: Clean Registry and Force Install
- 1If normal methods fail:
- 2Registry cleanup (careful!):
- 3regedit → HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall
- 4Also check: HKLM\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall
- 5Find the application by DisplayName
- 6Delete the entire key for the stuck application
- 7Also check HKCR\Installer\Products for orphaned entries
- 8After registry cleanup:
- 9Restart PC
- 10Run your installer again
- 11If installer supports force mode:
- 12msiexec /i "installer.msi" REINSTALLMODE=vomus REINSTALL=ALL
- 13Or: run installer with /force flag (if supported)
- 14Some installers accept: setup.exe /FORCE or /OVERWRITE
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