My Wii finds the network easily... strong signal but one Mac filtering is applied it will not connect

I've checked other posts but this seems different

I've checked the Mac address a lot and it also appears in my client list

If I disable mac filtering it connects staright away
(interestingly enough if I apply it again whilst the Wii is on it stays connected.. which I guess amkes sense)

Is there a trick or router setting I'm missing??