I am running the following test script to try to read packets from a sample .pcap file I have downloaded.

import socket
import dpkt
import sys
pcapReader = dpkt.pcap.Reader(file("test1.pcap", "rb"))
for ts, data in pcapReader:
    ether = dpkt.ethernet.Ethernet(data)
    if ether.type != dpkt.ethernet.ETH_TYPE_IP: raise
    ip = ether.data
    src = socket.inet_ntoa(ip.src)
    dst = socket.inet_ntoa(ip.dst)
    print "%s -> %s" % (src, dst)

For some reason, this is not being interpreted properly. When running it, I get

KeyError: 138

module body   in test.py at line 4
function __init__     in pcap.py at line 105
Program exited.

Why is this? What's wrong?