This is because there is still the remnants of a previous installation of the workshop manual on your system.
Here is a fix for you:
Open Virtual Box Manager
Right click on the virtual machine in the Virtual Box Manager
Click "Remove"
A pop-up will appear. Choose "Remove only" which will simply remove all traces of the virtual box from the Virtual Box Manager
Close the Virtual Box Manager
Using the file manager, browse to the folder containing the virtual machine
Delete (or move) everything EXCEPT the .vmdk virtual hard disk file
Open Virtual Box Manager
Click "Machine"
Click "New"
Name the new machine (you can use the same name as the one originally used)
NOTE: The name of the machine is will become the name of the directory that will contain the virtual machine so choose wisely and also note that if you want the .vmdk file to reside in the new directory that it will take additional steps in Virtual Box Manager
Select the proper Type and Version for the virtual machine that was having the issue and click "Next"
Select the memory size you want the virtual machine to have allocated and click "Next"
Select "Use and existing virtual hard disk file" and select it by browsing to it's location
Select "Create"
Simply follow the prompts from there and then start the virtual machine.
Everything should run fine now.
