MI4 - always get "error 5" trying to install driver


I recently bought a used MI4 usb interface, and I’m trying to get it to work for doing 4-channel recording. I’ve had no luck installing the 2.8.13 XP/Vista driver under both Windows XP and Windows 7 32-bit with the updated driver from here:
I’ve never installed any software that came with it, as I didn’t get any software with this device. All I have is the drivers downloaded from the steinberg.net website.

Every time I run the installer, it gets to the point where it asks you to plug the MI4 in, then after a minute or two it seems to continue with copying files, then fails with “Unfortunately the installation failed (error 5)”.

I’ve tried the older 2.3.8 and 2.5.3 drivers with the same result.

Can anyone tell me what “error 5” actually means, and what to do about it? How do I get this device to work?