How to reinstall an app purchased from the app store it it shows "downloaded"..

I wanted to open an app but the finder cabe back with a message indicating that it was damaged and that I should delete it and download it again from the App store. I deleted the program, but now, when I go to the App store the program is marked as "downloaded" and I can not install it again.

How do I reset the button so I can install the app again?