Does Windows see the device when you can connect via the Wireless-N network? If so, is it seeing the device in a different way to when connected via wireless-G?
Calibre is using the OS to connect to any device. Calibre needs the OS to be able to see the device and present it in an expected way. If the OS doesn't see it, calibre can't. Check if you can access the device from Windows, and if you can run the steps in
My device is not detected by calibre. Then, connect via Wireless-G, disable the driver being used by calibre, and run the last step again. The difference in what the OS is reporting to calibre for the two connection methods is probably the important thing here.