failed to communicate with camera

Hi, I have a Canon 5D that I have had for many years and have been using PC very succesfully when transferring images from the Canon 5D to the PC. I simply connect the USB cable from the camera to the PC and everything happens automatically. I just bought an Apple and when I plug the same Camera (via the USB) with the Apple Macbook Pro I get the following error "Failed to communicate with camera. Check connections". What does this mean. My Canon 5D is working 100% as it works with a PC and the USB cable is the same cable that works with the PC. PLEASE HELP!!!!