I found this:
https://www.virtualbox.org/ticket/18153
It looks like the fix for this issue, but have not tested as I do not know how to apply the patch.
I can eventually figure it out, but if anybody can explain or provide a link on how to apply a patch like this it would be very appreciated. Thanks
Spent all day messing with the same problem. Cannot use console in phpVirtualbox, Remmina, or TightVNC. I can ping the VM and access its shares via Samba so it is running normally.
This all happened after updating the VM and the Host before a restart of the server.
Also tried creating a new VM to make sure it was not an issue with this specific guest and got the same result.
