This is really frustrating and I'm sure there's a really simple explanation but sometimes after transferring pictures from my SD card in my camera the Mac can't seem to find them.... When i click on the photo in iPhoto i get a message that comes up saying "the volume for image ****** can't be found" and i have no f*****g clue why?
Did you eject the card from the desktop before removing it from card reader or unplugging camera, my mac doesn't like me doing this though I have never lost data it keeps warning me that I might if I don't.
try reloading pictures again,
and i have no f*****g clue why? 
