Unable to install VirtualBox 4.3.16 on Windows 7

[fraidiecat1]

My installation of VirtualBox 4.3.16 proceeds as expected until it is almost completed and then it rolls back the installation and reports a failure.
I had previously installed an earlier version of VirtualBox, which worked fine. I was prompted to update it 4.3.14 which failed. I then uninstalled everything and tried installing 4.3.16 from scratch. I have rebooted many times and checked that there are no VBox services running.
Attached is a ZIP file of the install log - can anyone tell me why it is failing?
(I had to ZIP The file as the maximum size allowed is 128K.)

[mpack]

It looks like it's failing to install a driver, probably due to a permissions issue. Make sure you run the installer using "Run as administrator", and Google for information on "Driver Signature Enforcement": yours should be set to at least prompt you if it's unhappy with the signing of a driver (i.e. don't just silently discard it).

[fraidiecat1]

Thanks for your reply!
I am an Administrator user on my laptop.
One thing that may be relevant is that I am seeing "VirtualBox USB" in the "Devices and Printers" Control Panel window, even though I do not have VirtualBox installed, implying that the old VirtualBox USB driver has not uninstalled correctly. I only see this when a USB memory device is attached to my laptop.
Is there a safe way to remove this 'old' VirtualBox USB driver before attempting to reinstall VirtualBox?