I can't remember where I found it, but here is what I have to do from time to time.
Disable your active network wired/wireless connection before cradling or attaching. Then hook up and WMDC sees the device. Once you do this, you can re-enable the network connection. Pain in the arse, but it works for me when WMDC will not see the device.
Apparently it's a know issue with MS that they are working with in the TCP/IP stack. I'll see if I can find the article, but that is the only thing that helped me.
Good luck!!