I just set up a NAS in a small office, there are some computers set up on a wired connection, and others on wireless.
I am able to access the NAS on the computers connected wirelessly, not the ones connected by ethernet.
The network is set up like this:
Internet --> modem --> wired router --> switch --> wireless router --> NAS
It is set up like this because the modem, wired router, and switch were set up first, then wanted to add wireless so an ethernet cord was run from the switch, away from the modem, to the center of the building and the wireless router set up there.
Are you using a single network or is the wireless router a second distinct network, i.e. is the wireless router just configured as an access point for the network or does it provide DHCP for the wireless network?
If you want to access the NAS throughout the network, the wireless router should only be acting as an access point on the same network as the wired router with an IP address that is in the network range but outside the DHCP assignment range or at least use a reserved dynamic address for the AP.