Failures of communication where Mosaic is unable to discover Rossini or loses it are usually caused by an issue with your network. If this is a new development have you changed something? Even if you have not done so to your knowledge, has there been an update to e.g. your router or switch software that originated with the manufacturer or supplier?
Edit: Looking back over the thread and as this issue has a bit if a history it may be worthwhile contacting dCs support as I see that one solution involved resetting the Network Streaming Interface: