The units themselves are faulty, I have 48 of them all exactly the same issues, no factory support I even went out and bought another to get free support, try this firmware, try that firmware. they do not know whats going on.
You might try a hard reset, hold the button in in the back for 10 seconds and when releasing all the lights should flash to indicate reset...
Here is my problem with wireless not working
http://forums.dlink.com/index.php?topic=12373.0