Windows Installer
1638
Another version of this product is already installed.
Needs attention
What it means
Windows Installer found an existing installation of the same product with a different version, and the package you are deploying is not configured to upgrade it. The install stops rather than creating two copies.
Real causes
- The MSI has no upgrade table entry for the installed version.
- A newer version is already present and the package refuses to downgrade.
- A previous deployment left a partially registered install behind.
What to do
- Find what is installed:
Get-ItemProperty HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\* | Where-Object DisplayName -like '*productname*' | Select-Object DisplayName, DisplayVersion, PSChildName - Uninstall the existing version first, then install the new one, in a single deployment sequence.
- If the vendor supports it, deploy the package that carries the correct upgrade code instead of the base MSI.
Where to look
- Application event log, MsiInstaller source
Checked against Microsoft documentation. Last reviewed 2026-08-20.
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