David, looking at the IP address that you are using it would appear to me that you are either using DHCP or Static IP addressing... this is of course fine... but and this is based upon the general rule that I have done this to myself too many times to count... is there a possibility that you have another network interface - say a wireless interface in the same IP subnet that is not actually connected to the Dante network?
A real world example could be - I configure my wired interface to 192.168.xxx.yyy for some reason as a static IP address (often times to mess with my switch settings) I then for whatever reason connect to a Dante - enabled device that could be set static, or be in a separate network with DHCP served addresses in that same logical subnet (this could be that I am using the same network device to serve addresses, and I simply didn't configure that part) I then have my Wifi connected to receive email, skype etc... the general things we do to stay in contact with the world...
The Router in my OS can see two interfaces - seemingly in the same subnet (after all it is working on IP addresses) - so it wrongly thinks it can communicate through either or both interfaces, because as far as it knows the packets will get to the same place (but in fact don't)
Best trick in the above would be to disable one of these interfaces...
let me know how you get on