problem using pcap

[datapath]

Hello
I am trying to learn to use libpcap, but Im having a few
problems. I found a good tutorial by Tim Carstens. There is
an example in the tutorial that I can compile with no
problems. When I try to run it on FreeBSD it doesnt capture any packet! And when I run it on Linux pcap_next returns imediately as if there was a packet, even if there was none!
Am I doing something wrong?

Thanks