I've just tested it and it worked for me:
Please, note that the text is only shown when you select a variation. So when you enter the page, and no option is selected yet, the text is hidden.
And when you start choosing options, the text is displayed and changes according to the selected variation.
And regarding your error. I'm not sure why happened. Perhaps it was when you added the text to a widget?
Anyway, I've added some extra logic to Multi-Inventory to prevent this from happening. This will come on the next version.