Error code 303019 means the connection to the Windows Store was lost or could not be made. The most common reason for error code 303019 is that the Windows Store is temporarily down. Usually it will come right back up shortly!
It also can mean your anti-virus program or firewall is blocking the game from talking to the Windows Store. Go to your anti-virus or firewall settings to make sure that it's not blocking your game from accessing the internet. If your anti-virus/firewall has an app "whitelist", you will need to make sure your Xbox enabled games are on this list.