Cisco VPN Client

Hello, I am wondering if anyone has experience with a VPN client that will connect but once a load is placed on the tunnel it crashes. by load I mean when the customer tries to connect to his email the tunnel will crash. this person half way around the world from me. If you have not experienced this do you have a suggestion were I could look to find the drop. I have check my pix log and my concentrator log but no luck there. while the person is connected a simple ping is approx 300Ms