Usually such a problem occurs with Routing issues. Check to see if the Subnet that you are talking about isn't directly connected to one of these devices with the whole network address. hope that helps.
At the pix side there is only one subnet & on the concentrator side their are 6 Subnets. Five of the subnets are able to communicate with Pix subnet but only one subnet is not able to communicate. After few hours automatically it starts working & then gets disconnected after few hours. When i tracert from this subnet it goes till the concentrator a stops.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...