One of the great features of the 17 " MBP, the Express Card 34 slot.
One of two things, the SSD is faulty or the slot connection has failed. Do you have another Express Card device such as an eSata connector to test the slot. By the same token, can you test the SSD on another MBP or do you have a second SSD to try.
Try a PRAM reset. (somewhat of a guess on my part)