Hi Paul.
I was going to suggest that you would find it in your profile, but it seems that you never logged it there.
Otherwise, if you bought it as a boxed set, it will be on the inside of the box or on the disk case. If you downloaded it via Vstep, it will be in the email you received.
Failing all else, if you have some valid proof of purchase, send it to Vstep at info@shipsim.com and explain the problem. Throwing yourself on their good and kind nature might just work. But you will need some convincing proof of purchase, of course.
