There isn't alot to go on here however it sounds like it is a compatibility problem between your machine hardware/software and Virtual box. You are the first I have heard of to report such a problem. You could try just starting the virtual the virtual box software (without the virtual machine)  to see if that starts without a problem to narrow things down a little. You could also re-import the ovf file taking care to follow the configuration instructions included in the CLSA course where you download the ovf file. There is also https://www.virtualbox.org/ which you can see if others with your hardware have experienced similar problems. And of course you can also change your player to VMWare player and import the ovf file to it and see if that works.