Hi Swamy,
while initiating a ping from one PC to the destination use the following ping x.x.x.x -t -l 1500 -f
This will give you message that the packet is to be formatted
Keep decreasing this value till you come across a value which allows you to ping through the tunnel.
Then issue the command sysopt connection tcpmss {value}
THe value you got from the ping.
HTH
Hoogen
Do rate if this helps :)