I have found that the iMXs board (and some other .net MF boards with AT91 and STM32 cpu) failed to receive the assigned IP address from D-LINK router (DIR-655). From the router, it stated that it has already assigned the IP to device, but the device showed 0.0.0.0 only. If use static IP, the device can connect to the network without problem.
However, it works fine with other router, like LinkSys, IP address obtained. I have found similar problem has been reported on netduion too.