I have found that Norton Smart Firewall and DLNA do not play in the sandbox very well together! For Mezzmo, and it appears most DLNA servers to work properly Norton Smart Firewall must be turned off. I had discovered this on my own system, and confirmed it via a number of posts on forums.

The bottom line is if you are having problems connecting to Mezzmo and have Norton Smart Firewall running, turn it off!