Make sure that all of the letters are capitalized. On the Windows version they do not need to be, but for the Mac it is required. It must be entered exactly as it is shown on the receipt, so include the hyphens. Sometimes copy/paste can pick up extra spaces or characters, so if copy/paste is not working, try to type it in manually. If there is a space before or after the key, that too will keep the activate button from showing up.