Chris Millard has an excellent utility for getting past that annoying 1704 error message:
Sometimes, Microsoft's Windows Installer package does not always uninstall a program properly, and even if you try and reboot your PC, you'll get the following error:-
"Error 1704. An installation of My Program v1.0 is currently suspended. You must undo the changes made by that installation to continue. Do you want to undo those changes."
Sometimes, even if you say Yes, the error keeps reappaering.
E1704C will clear the registry entries that prevent further installations of any packages that use Windows Installer.
E1704C will NOT actually install any software on your PC. It will just modify the Registry key that is stopping you from installing any more packages.