Well I just did some light research and you wouldn't happen to have a Intel wireless NIC would you? Found a bunch of forums post on egghead, DSLreports, PSN, Wii Forum, etc, all with issues between D-link routers and Intel cards. Intel cards are super common though, so could mean nothing. Eitherway, heres some tips I dug up will searching.
1. Turn your off the Power Saving Protocol (PSP) on your laptop. This might also be known as setting it to CAM or Always Awake. More info here: http://www.intel.com/support/wireless/wlan/sb/cs-006205.htm
OR (because this kills battery life)
2. Lower the Beacon Period: 192.168.0.1 > Advanced > Advanced Wireless > Beacon Period.
Default is 100. Some people have better results with a Beacon of 30 or so. Picture the beacon being like schronizing your watches before a mission. The more times you do it during a mission, the more cordinated you will be.
AND
3. Increase your DTIM: 192.168.0.1 > Advanced > Advanced Wireless > DTIM Interval
DTIM is the amount of frames a wireless client (Wireless NIC) waits before it "wakes up" to transmit or recieve data. Default is 1. If your lowering the Beacon to improve dependability, increasing your DTIM can perserve battery life.
Basically here is the deal. Theres some different technology out there to peserve battery life. The core of it to not have the laptop listening for anything when the router isn't sending, and not have the laptop sending when the router isn't listening. When all things are perfect, it works great. But its like fireflies trying to use morse code in a forest jack full of fireflies. When you have so much noise, the system can start to become inaccurate. The looser you make that power saving system, the more dependable (and better performing) it becomes, but the more battery you burn. If this is a wireless desktop or a laptop thats plugged in all the time there is no reason for PSP to be enabled.
Keep in mind this is one possibility of varible in your problem. There may be, and probably are, other parameters as well. Thats why its important to start with a router that is default and a wireless NIC with updated driver with default values. Change one thing, monitor, evaluate, change it back, repeat.