Can't uninstall VIPRE Enterprise under Vista Enterprise 64bit

I manually deployed VIPRE Enterprise to a laptop running Vista Enterprise 64-bit. The laptop is rarely in-house connected to our network. VIPRE didn't seem to be running, wasn't getting any updates, and didn't have an icon in the system tray.

I upgraded our VIPRE Enterprise Server and created a new deployment MSI. I want to re-install the agent on this laptop. When I try to run the MSI file, Windows tells me that the application is already installed and that I need to remove it using the Control Panel. When I try to uninstall it, however, the uninstall hangs. The same behavior happens even after a reboot.

How can I get the latest agent to install on this laptop?