When I Google ...... AVOS/1.1 libhttp/1.1
I get a site about Kodak Easyshare Wireless Picture Frame.
Do you have one of these devices in your network?
When you get the error message, does mp3 playback stop? If you have this device in your network and playback stops when you are alerted of the error, you could try disabling the device, and see if it makes a difference.
I get traces of unrecognized media renderers, such as WMP server, and my room-mates random devices, but it has never been the cause of problems. In fact I see an "unrecognized renderer" on my Status Tab right now, but it has no ill effect on my setup.