You can get that RSA Key warning when you have the same IP address defined for different devices. A kindle touch using SSH in diags mode looks like a different device from when it is booted in main mode (using simple USBnet).
Your authentication failure is happening in your host PC. The error messages says what you need to do. You need to edit /Users/Dani/.ssh/known_hosts like it says. You will need to do that each time you try to connect from a different device or bootmode that uses this IP address, or do a more permanent solution.