Pcap.Net just wraps WinPcap so it has the same behavior in that sense.
If WinPcap will see the packets, so would Pcap.Net.
Try sniffing the packets using Wireshark and see if you can see them.
If you can't, it has nothing to do with Pcap.Net and you should investigate on WinPcap or McAfee sites.
Sorry for not being able to be more helpful,