Having same problem with WCR-GN.
Just purchased the unit a week ago. Upgraded firmware to latest on first day and configured it as a access point as I have a very complex Linux firewall protecting several different servers doing many different things, Several web servers, dhvp server, etc..
Seems to be a problem tied to mixing devices that can do G and N wireless protocols. If all the devices are one or the other then things work just fine. But when more then one protocol starts working at the same time things slow down, etc. If I use my Notebook and 3gs no problems at all. If we connect both iPod touch 4's no problem but mix 3Gs and iPod touch 4 or notebook and iPod touch 4 and one or both devices suddenly we have issues. Internet connections suddenly go away or slow to beyound a crawl. Apple products complain they can't contact the internet. Go to settings screen and watch the network and it will suddenly say there is not a IP if you want a minute or two with something downloading in the background many times.
FYI also have a nook and it complains when we start mixing protocols... If there was a way to disable N via the interface I'd try that to see if the problem goes away but there is not a option. Yes defeats the purpose of purchasing a B/G/N router/access point but I'd be willing to try it as a test...
FYI: it is NOT a channel issue, the only other wireless device anywere within a quarter mile is on Channel 11 and I'm using 1.
Yes iPhone/iPod's will drop IP and transmision within seconds of sleeping and re-connect when woken. That seems to be a part of the issue. Older D-Link never had issues (granted it only did B and G, no 802.11N which the iPod Touch can do according to your client monitor screen). If I could go back to the D=Link I would at this point BUT it died so purchased this as it was on special.