I have a problem with a PIX 501 that allows you to establish a VPN session to a remote network (using the Cisco VPN client software) but does not permit you to ping any devices on the remote network. This problem only occurs with the PIX. I have similar environments not running PIX firewalls that do not have this problem. If I replace the PIX with a non Cisco firewall, the problem goes away or if I create a site-to-site tunnel, I can then access the remote network.
I have this problem too.