That's a tough one, not knowing what kind of Macintosh you have, what make and model of camera you have, what version of OS X you're running, and how exactly you're trying to download photos from the camera (Image Capture, iPhoto, Aperture, etc.).
Please give more detail so we can begin to troubleshoot your problem. Right now, all we know is that you have some kind of digital camera and something (the computer, some piece of software, some evil gnome who lives in the wall, etc.) is telling you something about some errors.