When trying to install on vista 64bit. I received this error message: "windows installer service could not be accessed" I tried many things...nothing worked.....But this one did... http://www.windowsbbs.com/windows-vista/82460-vista-home-premium-x64-installing-itunes-solution.html Go to this registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSIServer Look for WOW64 and it's value. Is it 0x00000001 (1) ? This value tells Windows Installer only to deal with 32-bit installers and to return you an error whenever you try to install something that is 64-bit. To fix it, just set the value to 0. So you will see in your editor: WOW64 REG_DWORD 0x00000000 (0) After changing the value to zero, restart your Windows Installer Service by using services.msc or reboot. This simple solution of changing the 1 to a 0 allowed me to finally install eset on Vista 64. Hope this helps some other poor soul.