If you are installing the latest version (0.21) version of TweetDeck and keep getting the following message…
The application could not be installed because the AIR file is damaged. Try obtaining a new AIR file from the application author.
Make sure that you have at least Adobe Air 1.5 installed. After installing AIR 1.5 if TweetDeck installation still gives you the above error then first install TweetDeck 0.20. Afterwards when you run it, it will tell you that an upgrade is available, go ahead and install. The upgrade should work now. Congratulations, you are on the latest version! 🙂