Virtualbox gives me the following output:
Failed to open a session for the virtual machine 8.
The VM session was closed before any attempt to power it on.
Result Code: NS_ERROR_FAILURE (0x80004005)
Component: SessionMachine
Interface: ISession {7844aa05-b02e-4cdd-a04f-ade4a762e6b7}
Edit: The option "Discard Saved States" is disabled.