Have you bought a Version 3 Activation Key? Older Activation Keys will not work in Stitchmastery Version 3.
You can get one for free if you have previously activated Stitchmastery – go to our website Shop page, add the Stitchmastery Version 3 Activation Key to your basket, and add your old Activation Key as a coupon code at the checkout. You need to put in all numbers/letters, hyphens or dashes, exactly as they appear. This will make the price of the new Activation Key £0. Follow the check-out process and a Version 3 key will be emailed to you.
Read more about how to do this here: https://www.stitchmastery.com/upgrade_to_V3.