This is happening because the application doesn't support streaming yet. As it is stated on the Google Play application's page, even if the Chromecast SDK is available, the application can't stream to TV devices due to technical limitations. However, to fix your problem, try using another application that has the same functionality. I suggest you take a look at Streambels AirPlay or AllCast. Both of these application have a large range of devices that can stream to. Also, before you install any of them, I suggest you use Google in order to find more about the DLNA Support.
