Did you try to re-download the game as well looking behind all windows to see if the code box is hiding behind them?

If you did, and it still doesn't work, as it states in the post (and later in that thread) I linked you to, we'll need additional information, as we have never been able to recreate this issue on any of our lab computers.

Have you used this particular computer to install and activate other LDW games, and did they work? What version of Windows are you running, and what security software are you using? If you have another computer available in your household, you could try installing it and activating it there as a test.