Billion 7800N wireless router and Netgear WN2000RPT issues

Before I recently bought my Billion 7800N wireless router, my Netgear WN2000RPT Wi-Fi Extender was communicating perfectly with my Netgear DGN2000 wireless router but with the Billion, the light above the other two lights (signalling the connection status between the router/gateway and Extender) remains red - even though it lets me connect to the Internet.

The Wi-Fi Extender is in my bedroom and my Billion router is downstairs next to our cordless phone.

I've tried moving the Wi-Fi Extender into mum's bedroom, where it's almost directly above the router but I still get the red light showing (occasionally an amber light).

Does anyone know why I'm having this problem when the Billion's got 3 antennas, so an excellent wireless signal?