Hi Anoop,
I took a look at your service (thanks for providing the URL) and tried adding it to the Sandbox myself. The communication error is due to your service not implementing CORS and thus your browser is blocking your computer from communicating with the service. Here is an example CORS configuration you can return temporarily to get things work. You'll want to change these values if/when you go to production:
Access-Control-Allow-Credentials true
Access-Control-Allow-Headers Authorization, Content-Type
Access-Control-Allow-Methods GET, POST, OPTIONS
Access-Control-Allow-Origin *
Access-Control-Expose-Headers Origin, Accept, Content-Location, Location, X-Requested-With
As an aside, take a look at the developer console in your browser as it generally will show you more details as to what is happening. For instance, in Chrome this can be found in View -> Developer -> Developer Tools. :-)
Best,
Kevin