Purchased game through Humble Bundle, after update needs Serial Key

[saraija]

I purchased the Humble Indie Bundle V about a week ago. I played through Amnesia: The Dark Descent and wanted to move on to Amnesia: Justine, but did not see the launch button. I downloaded the game update (1.7, I think) from the site and installed it. Now when I try to start the game, it asks for a serial key.

Is there a way to find this?

Should I uninstall completely and then reinstall?

Was the "Justine" button there all along, and I was too dumb to notice it?

Any help is appreciated.