short post after Summer vacation 🙂 A customer had the problem that he couldn’t install msxml4 sp3.
During installation the setup could not register type library C:\Windows\SysWOW64\msxml4.dll.
The reason was that he had disabled application compatibility engine by policy via registry:
Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\AppCompat] "DisableEngine"=dword:00000001
or by Group Policy Object Editor
Solution is to enable the Application Compatibility Engine.
c:\> reg add " HKLM\SOFTWARE\Policies\Microsoft\Windows\AppCompat" /v DisableEngine /t REG_DWORD /d 0 /f
or by GPO Editor