Windows 7 VM fails to start after host OS upgrade to Sierra 10.12.4

[RAlex]

My Windows 7 (64 bit) Virtual Machine was working fine on Mac Book Pro El Captain host till yesterday. After I chose to upgrade to Mac OS Sierra 10.12.4, VM fails to start. My Virtual Box version is 4.3.30 r101610.

Following is the error message:

Failed to open a session for the virtual machine Windows 7.
The virtual machine 'Windows 7' has terminated unexpectedly during startup with exit code 1 (0x1).

Result Code: NS_ERROR_FAILURE (0x80004005)
Component: Machine
Interface: IMachine {480cf695-2d8d-4256-9c7c-cce4184fa048}

Could someone please help me resolve the issue? I would like to know the best approach before I try reinstalling the Virtual Box/Virtual Machine.

Thanks in advance.

[socratis]

My Virtual Box version is 4.3.30 r101610.

That's too old for 10.12.x. Download the latest and greatest (5.1.20 as of this writing). Use the "VirtualBox_Uninstall.tool" in that DMG, and then install the new VirtualBox. Your VMs will be unharmed.

EXCEPT, if you have a VM in saved state. That might cause problems (most probably, because it's a big version leap). If so, then simply discard the saved state.