Currently, IP version 6 (IPv6) is not supported on any of the Cisco VPN concentrator models for defining the interesting traffic.
If IPv6 traffic must be carried over an IPSec tunnel, add more Access Control Lists (ACLs). These ACLs are in a completely different format. When the ACLs are not configured, the VPN devices drop packets because the packets do not match the IPSec traffic previously defined.
PIX Firewall 7.0 does allow you to configure ACLs using IPv6 addresses. For more information on this, refer to Configuring IPv6.