Been getting strange behaviour from my N800.

I have had it set up on my home wireless for years, today its connecting like normal but the connection (and contacts) keeps loosing connectivity.

I use mac filtering so went into my router setup via my laptop and the N800 is sitting awaiting approval as an unknown device and the mac address field is blank.

I think the problem must be that its not giving my router its mac so the router is blocking it as an unknown device.

Any idea why my N800 would stop giving out its mac?