The red 'No' symbol in the bottom right corner of the 851N display (please see below) indicates that the unit is connected to your network but not the internet. This may mean that you are able to stream audio from NAS drives and computers but not play internet radio.
The streamer will check the stability of its internet connection by 'pinging' Googles DNS servers. This ensures that the unit is fully able to access all relevant entertainment content without issue. This check can be prevented by firewalls, ports being blocked etc. within your router.
If no firewall is active and the problem persists we would suggest that you contact your internet provider regarding this.