IP Sec tunnels: Ends of the tunnel cannot ping each other

Can you post screenshots of your VPN Tunnel? 

No need.

Everything is fine now.

I changed something on the FW rules that regulate incoming traffic at both ends.

I enabled NAT. 

And I was able to do traceroute and PING

No need.

Everything is fine now.

I changed something on the FW rules that regulate incoming traffic at both ends.

I enabled NAT. 

And I was able to do traceroute and PING

Basically you do not need NAT for VPN... So this is just a workaround for the current issue. 

Seems like the gateway is not correct configured and the client cannot respond to the traffic coming from the VPN. So NAT (MASQ) resolve such issues. 

I concur with ManBearPig here that NAT should not be required.

I am interested to see what the connection detail is for the VPN session.

Here is some screen shots of some functioning VPN Firewall rules I use.

Out to VPN

In From VPN

and obviously making sure you have similar rules on the other firewall.

True.

The ISP has issues. Resolved it already. Thanks