Error code: 1638 – ERROR_PRODUCT_VERSION

Error description: Another version of this product is already installed. Installation of this version cannot continue. To configure or remove the existing version of this product, use Add/Remove Programs in Control Panel. Resolution: When you try to uninstall an application, you get the error message: “Another version of this product is already installed.” with error code 1638. This has to do with major and minor versions of the application. When the PackageID of an msi package changes , it will detect itself as a different version. Remove the Windows Installer registry keys from this application. These can be found under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\{SID}\Products.
Delete the corresponding subkey (GUID, or rename it to {GUID}.bak) and try to delete the existing application with the new MSI.