Question : UP-NO-IKE session Status on IPSEC VPN

I am currently trying to setup a VPN between our VPN router and one of our customers routers, but we have been having some issues. The customer is trying to activate the VPN by sending ICMP packets to a server within one of our datacentres but it does not appear to be bringing the VPN up. In order to test this from our end I have created a loopback interface on our VPN router with the ip address of the server that they are trying to reach and I have pinged the NAT'd address of the customer. I have been able to get a response from the address and the VPN now shows a state of UP-NO-IKE. Does anyone have any idea what this message indicates and why I am having the problem that we are having.

Any help would be greatly appreciated

Answer : UP-NO-IKE session Status on IPSEC VPN

The problem appears to be with the Third parties VPN configuration. They have since resolved this and the VPN appears to have been stable for a while now. Thanks for your help anyway :)