I control one side of this - Cisco ASA 5505 running 8.4+. I do not know what type of device on the other end.
Outside: 184.108.40.206/28 <-- not the actual IP.
I have an IPSec tunnel to the remote side The local side is a single host (192.168.1.1), which I am NAT'ing to one of our public IP's (220.127.116.11).
Likewise, the remote side is NAT'ing to an IP as they enter their side.
My host (192.168.1.1) can successfully ping the IP's on the inside of the remote tunnel.
The remote side, however, cannot ping 18.104.22.168.
If a packet-tracer and actual pings from the host on my end suggest it's working, does it seem like the problem is on the remote side?