Cannot Start VirtualBox Virtual Machine after an Upgrade

Having upgraded Oracle Virtualbox on a Windows host, I found that I could not start any Virtual Machine instances. VirtualBox displays a dialogue window with the error message shown below,

Examining the virtual machine log file, i.e., Logs\VBoxHardening.log in the Virtual Machine instance directory, I found the following error message near the end of the log file,

1660.6c38: supR3HardenedVmProcessInit: Opening vboxdrv stub...
1660.6c38: Error opening VBoxDrvStub:  STATUS_OBJECT_NAME_NOT_FOUND
1660.6c38: supR3HardenedWinReadErrorInfoDevice: NtCreateFile -> 0xc0000034
1660.6c38: Error -101 in supR3HardenedWinReSpawn! (enmWhat=3)
1660.6c38: NtCreateFile(\Device\VBoxDrvStub) failed: 0xc0000034 STATUS_OBJECT_NAME_NOT_FOUND (0 retries)

Driver is probably stuck stopping/starting. Try 'sc.exe query vboxdrv' to get more information about its state. Rebooting may actually help.

The message indicates that Windows service vboxdrv, i.e., the Virtual Box Driver has some problem. Following the advice in the log, I issue sc.exe query vboxdrv in a Windows Command Prompt window,

C:\>sc start vboxdrv
[SC] StartService: OpenService FAILED 1060:

The specified service does not exist as an installed service.
C:\>

which indicates that Windows service vboxdrv does not exist. To fix the issue, I reinstalled the driver vboxdrv from the directory C:\Program Files\Oracle\VirtualBox\drivers\vboxdrv. From the Windows GUI, you can right click the VBoxDrv.inf and choose "install".
If the installation is successful and you query the driver status again, you should see something similar below,

C:\>sc query vboxdrv

SERVICE_NAME: vboxdrv
        TYPE               : 1  KERNEL_DRIVER
        STATE              : 4  RUNNING
                                (STOPPABLE, NOT_PAUSABLE, IGNORES_SHUTDOWN)
        WIN32_EXIT_CODE    : 0  (0x0)
        SERVICE_EXIT_CODE  : 0  (0x0)
        CHECKPOINT         : 0x0
        WAIT_HINT          : 0x0
C:\>

Now I can launch the virtual machine instances.