Firstly go back and check everything you've done to secure your network, I suppose this was done on the wireless router connected to the WAN device. But what about the far-off wireless router, it also requires configuration.
A wireless router is in effect a wired router with an access point.
So you have two access points on your network. Can the wired PC and wireless PC on the far-off network ping each other?
See if you can find any resource of an access point connecting to an access point, you're probably just missing a setting somewhere on your router.
I also use a wireless network with a wireless router and these things can be temperamental, sometimes the wireless PC cannot connect to the wireless router, then it requires a tickle to go on.