Installing Security Essentials on Vista 32-bit

During install I hit error 0x80070643

Looking in the log file (MSSecurityClient_Setup_epp_Uninstall.log) shows the following info for 'return value 3':

Action start 19:07:45: InstallValidate.

MSI (s) (6C:6C) [19:07:45:190]: Note: 1: 2205 2: 3: _RemoveFilePath

MSI (s) (6C:6C) [19:07:45:190]: Note: 1: 1321 2: C:\Program Files\Microsoft Security Client\CleanUpPolicy.xml

MSI (s) (6C:6C) [19:07:45:190]: Product: Microsoft Security Client -- Error 1321. The Installer has insufficient privileges to modify this file: C:\Program Files\Microsoft Security Client\CleanUpPolicy.xml.

Action ended 19:07:45: InstallValidate. Return value 3.

Action ended 19:07:45: INSTALL. Return value 3.

MSI (s) (6C:6C) [19:07:45:190]: Windows Installer removed the product. Product Name: Microsoft Security Client. Product Version: 2.1.1116.0. Product Language: 1033. Removal success or error status: 1603.

I've tried following suggestions in other threads (Windows is up-to-date, completely removed previous antivirus/anti-malware software, Windows Installer service is running, installing the correct version of MSE, used Selective Startup mode).

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