Does your reader work for other cards, or indeed do you have another reader/computer you can try it in? I would expect to see that more with a bad reader or USB.
It is not impossible that the SD card decided to fail at that moment, or one preceded the other, but if those are the error results I would be surprised for it to be the hacked device you were running it on that normally does SD quite happily. If it was some hack job reader that applied too many volts then so be it but it is still a switch and your PC that were speaking to it.
Depending upon the particular failure that happened to cause that then there still may be means of dragging the data back, it is fairly slow and quite exotic as these things go (short version is SD cards tend to have two modes of operation, if the controller crashes for one which would happily show what you see there then you might still have the other).
http://hackaday.com/2013/08/19/rescuing-an-sd-card-with-an-arduino/ being nice jumping off point into that world.