virtual box linux guest dead after host MacOS autoupdate while guest was running

I know that I should have powered off the guest, but I was away from the computer when a forced update occured to MacOS host.

At first the manager said the virtual machine was still running when it was not.

I then right clicked to save it, then tried to go back to it and it didn't work

I then discarded the saved sate and tried to restart and got the same error

The virtual machine 'xxxxxxxxx' has terminated unexpectedly during startup because of signal 6.

Result Code: NS_ERROR_FAILURE (0x80004005) Component: MachineWrap Interface: IMachine {5047460a-265d-4538-b23e-ddba5fb84976}

Any suggestions would be very gratefully received,

Ok so I don't know why, but this was fixed by finishing updates on the host Mac OS and rebooting....