The server you're trying to connect to didn't respond quickly enough. Some don't, because they're temporarily down, a forum is doing a database backup, the webmaster is making a few changes and forgot to repoint that URL to a page that says "Sorry, we'll be down for maintenance for a few hours", that sort of thing.
Usually it means "this package isn't for your hardware.version of Android. The developer checked the wrong box." Sometimes it means that you got a bad download, and the phone really can't parse (read) the package.
If downloading it gain doesn't fix it, contact the developer. But don't hold your breath. Some developers could write the Obamacare site in their sleep (seriously - it's tons of code, but not difficult code), others couldn't program a wet tissue to fall apart. And some have abandoned the app, the email address no longer works ... bottom line in those cases is to find a different app.
