USG20 will not respond to windows server

Graham

I have a USG20 set up for Site to Site VPN. At site 1 there is a windows server 2012. The USG will not respond to the server. It will respond to the other computers on the network. So if i am on the server and I ping the router, i am able to see the packet on the interface using wireshark. I am not getting a reply. Capturing the data on the USG20 I can see the ping arrive and then nothing. 
If I ping from any other computer in the office I get replies back. When I look at the captured data I can see the ping coming into the USG and the reply being sent out again. 
So every computer on the network has internet access through the USG20 but for some reason the Windows Server does not as the USG20 seems to be ignoring all traffic from it. 
The server can ping any other computer on the network and get replies no bother. 
The Server is set up with a Static Ip address outside the DHCP (USG20) scope

Zyxel_Charlie

Hello Graham,
In the VPN case, the ping service should be fine between computer and USG. 
For analysis the case, please share the topology with IP to  me(just draw and share it).
Secondly, I want to know if the ping service did not respond to server, which PC(IP) receive it?
Thirdly, is there any routing rule in your configuration? (please pm me you configuration for checking.)
Charlie