Hi, welcome to TSF
Download the
MSXML4 SP2 update. Don't install yet.
Close down all running programs and uninstall Flight Sim from Add/Remove Programs. Reboot and log on again with
full Admin rights (very important for this type of error).
Go to Start > Run >
msconfig > General tab and select Diagnostic Startup. Then click the Services tab, scroll down to the
Windows Installer entry in the Services column and enable it by clicking its checkmark box. Click OK to close msconfig and reboot.
Install the downloaded MSXML4 SP2 update by clicking it.
Go back into msconfig > General tab and set it back to Normal Startup. Reboot to complete, then try installing the game again.