WINDOWS INSTALLER ERROR · ERROR_PRODUCT_VERSION

Error 1638: Another Version of This Product Is Already Installed

The setup found that another version of the same product is already installed, and Windows Installer does not continue with this one. Microsoft's text tells you where the existing version is configured or removed.

WHAT WINDOWS SAYS

Another version of this product is already installed. Installation of this version can't continue. To configure or remove the existing version of this product, use Add/Remove Programs in Control Panel.

Wording from Microsoft's documentation, linked under Sources.

TECHNICAL SUMMARY

Number	1638
Windows name	ERROR_PRODUCT_VERSION
Where it appears	Exit code of msiexec.exe
In PC Tweaker Uninstaller	Install-time error

What causes Error 1638

Another version of this product is already installed: that is the whole of Microsoft's text, which adds that the existing version is configured or removed through Add/Remove Programs.

How to fix Error 1638, safest step first

Microsoft's message names the tool: the list of installed programs. Look before you remove anything, because the version you have may be the one to keep.

See which version is installed
Open Settings > Apps > Installed apps and find the product; the version is shown under its name, and the check below prints it too. If the installed version is newer than the one you were installing, check whether the program that asked for it already works before changing anything.
To undo: Nothing to undo: you only looked.
Keep the installer of the version you have
Before removing a version, make sure you can get it back: keep its setup file or note where to download that exact version.
To undo: Nothing to undo.
Uninstall the existing version, then install the one you want
In Settings > Apps > Installed apps, uninstall the existing version, restart, and run the new setup. This is the route Microsoft's message describes.
To undo: Uninstall the version you just installed and install the previous one again from the setup you kept.

Check it yourself, without changing anything

List installed Windows Installer programs with their versions (PowerShell)

DisplayVersion is the installed version; compare it with the version of the setup you are running. Nothing is changed.

Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*',
  'HKLM:\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*',
  'HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*' -ErrorAction SilentlyContinue |
  Where-Object UninstallString -match 'msiexec' |
  Sort-Object DisplayName | Format-Table DisplayName, DisplayVersion, PSChildName

PowerShell

02
Read what Windows Installer logged (PowerShell)
Microsoft documents event 1033 (installation completed with status) and 1034 (removal completed with status): each names the product, its version and the status number, which is 0 on success. Nothing is changed.
```
Get-WinEvent -FilterHashtable @{ LogName='Application'; ProviderName='MsiInstaller'; Id=1033,1034 } -MaxEvents 10 |
  Format-List TimeCreated, Id, Message
```
PowerShell

What PC Tweaker Uninstaller does with Error 1638

Install-time error

Error 1638 belongs to installing, so the Uninstaller does not produce it. It can do the step Microsoft's message asks for, removing the existing version, and before that it shows the exact command and its Confidence Score, which flags system components and runtimes other software depends on. If the version already installed is a shared runtime, read that warning before you remove it.

PC Tweaker Uninstaller: see the exact command before a removal runs

Common questions

Do I have to uninstall the other version?

Only if you need the version you were installing. Microsoft's text says the installation of this version cannot continue and points you to the existing one; it does not say the existing version is faulty.

Why does error 1638 appear with runtimes and redistributables?

Because several programs can ship a setup for the same shared component. When a different version of that product is already installed, Windows Installer stops with 1638. Check the installed version first: other programs may be using it.

Where is Add/Remove Programs on Windows 11?

Microsoft's text uses the old name. On Windows 11 it is Settings > Apps > Installed apps, the list Microsoft's current support page uses for uninstalling.