I think I have arena set up correctly (see screenshot).
I've loaded in some 2d data, some trajectorized data and a skeleton, turned on and off all the streaming options and still don't get any data coming through.
I used wireshark to look for any output and there don't seem to be any UDP packets being spontaneously broadcast.
If I request a packet with NAT_REQUEST_FRAMEOFDATA the packet I get back seems to be malformed (my machine is 129.215.91.222 and arena is on 129.215.90.205) (see screenshot):
Arena is running on Windows 7 pro.