VPN Tunnel with Policy NAT

I have a Cisco ASA 5505 configured with four VLans.

VLan4 - 10.0.0.0/24

I also have a Policy NAT in place that masks all outgoing traffic from VLan4 across a specific VPN tunnel to 10.10.42.0/24

The VPN tunnel is up and I can ping the remote host, but they cannot get a response from me.

They need to be able to ping the 10.10.42.0/24 network, which exists only to disguise 10.0.0.0/24

Is this possible considering the subnet they are trying to ping doesn't actually exist.

How do you send traffic back across a tunnel when a policy NAT is used?

Here is some of my config:

interface Vlan4
 nameif XXXX
 security-level 50
 ip address 10.0.0.1 255.255.255.0

access-list inside_nat2_outbound extended permit ip 10.0.0.0 255.255.255.0 host  X.X.X.X
access-list inside_nat2_outbound extended permit ip 10.10.42.0 255.255.255.0 host X.X.X.X
access-list VPN_SITE3 extended permit ip 10.0.0.0 255.255.255.0 host X.XX.X
access-list VPN_SITE3 extended permit ip 10.10.42.0 255.255.255.0 host X.X.X.X
access-list inside_nat10_outbound extended permit ip any any

global (outside) 2 10.10.42.0
global (outside) 10 interface

nat (AS400) 2 access-list inside_nat2_outbound
nat (AS400) 10 access-list inside_nat10_outbound