There's LOTS of forums where you will read about connectivity issues with D-Link routers and this one specifically. They key seems to be taking some of the variables away from the router, at least on the 802.11 side.
Since I don't have anything that uses 802.11n (and since this seems to be one of the weaker points of this router anyway), what really helped me was to take "N" out of the equation. Go to Setup | Wireless Settings | Manual Wireless Network Setup and change the 802.11 Mode to Mixed 802.11g and 802.11b.
(Yes, I have an SSID for my system, but I erased it from this screen shot. I guess I just paranoid!)
Some people report having better luck by un-checking the Enable Auto Channel Scan and trying specific channels to see if one works better than the other.
Also, this particular D-Link is known not to have the greatest range so that may be an issue as well.
Hope this helps!