Help required in operating tunnel.py

Hi,Whenever i run the tunnel.py example in digital folder i face a
problem.After following the procedure to run tunnel.py i observe that i
do transmit packets but i do not receive any packets on one machines.I
get the following message :
Tx: len(payload) = 227Tx: len(payload) = 182Tx: len(payload) = 215Tx:
len(payload) = 255Tx: len(payload) = 54Tx: len(payload) = 70uUTx:
len(payload) = 182Tx: len(payload) = 90Tx: len(payload) = 70

when i ping the other machine i get following message :
From 192.168.1.102 icmp_seq=6 Destination Host UnreachableFrom
192.168.1.102 icmp_seq=7 Destination Host Unreachable
I am using ubuntu 9.10.
Please help me.
Cheers,Chuck.