I'm on Windows 7 64bit, with MSE, with version 4.3.16, and I get the following error each time I try to start a VM:
Failed to open a session for the virtual machine Test.
The virtual machine 'Test' has terminated unexpectedly during startup with exit code 1 (0x1). More details may be available in 'C:\Users\Owner\VirtualBox VMs\Test\Logs\VBoxStartup.log'.
Result Code: E_FAIL (0x80004005)
Component: Machine
Interface: IMachine {480cf695-2d8d-4256-9c7c-cce4184fa048}