Using vpnc from command line, not with network-manager.
I had this problem already in 8.04 and found a workaround back then, stupid me doesn't remember what I did to fix that, though. Probably something mentioned in here previously.
However, since 8.10 I start to have this problem again.
Nov 4 12:03:05 xxxx vpnc[19269]: connection terminated by dead peer detection
Confirm, this is not solved in 8.10.
Using vpnc from command line, not with network-manager.
I had this problem already in 8.04 and found a workaround back then, stupid me doesn't remember what I did to fix that, though. Probably something mentioned in here previously.
However, since 8.10 I start to have this problem again.
Nov 4 12:03:05 xxxx vpnc[19269]: connection terminated by dead peer detection