Hi fatherb,
I’m not sure if it’ll work for you but I had the same problem, and after a quick search on the plugin’s FAQ (http://yithemes.com/docs-plugins/yith-woocommerce-zoom-magnifier/08-help_faq.html), they mentionned :
If you activate the plugin after you have uploaded the images of the product, you need to regenerate the thumbnails before using it.
And although I did it the other way (I activated the plugin first, THEN uploaded the images), everything worked fine after I actually regenarated the thumbnails.
How to do it : http://www.wpbeginner.com/plugins/regenerate-thumbnails-new-image-sizes-wordpress/.
Hope it helped.
Wow, thanks Woopsy. That did the job.
I’m glad everything’s fine now. 🙂