If it's erroring out, you won't see it since the MSI is being run silently. Does it install OK after the fact? If the problem persists after Windows installs, then you can try decompressing it and running the MSI directly. At least then if it fails, you'll get an error message. If it passes post-install, you've probably got an error in your syntax somewhere. I don't use RunOnceEx, so I'm afraid I can't be of any more help than that, though. BTW, I'm assuming you renamed the exe from netfxsp1.exe to netfx.exe