Game not starting?

[Ludicus]

When I try to start the game, I get the cd-key prompt. When I launch the game, I get "Preparing to launch..." then it disappears and opens the cd-key window again. I checked the box so I don't see it again, now when I start to play it I get "Preparing to launch...", then it disappears and appears again, then I get a "Application already running" error. What might be the problem?