I'm trying to load my pictures onto our iMac computer, and my camera says "communication error". I've never had this problem before, and have always been able to load pictures just fine onto our computer. How do I fix this?

Consider NOT connecting your camera to your computer.

The best way to download pictures from your camera to your computer involves removing the memory card from the camera and plugging it into a card reader (either built-in to the computer or connected via USB or FireWire). This is likely to be faster than connecting the camera to the computer, and won't run down your camera's batteries.

Once the card is plugged in, it will appear to your computer as a removable drive. You can use the operating system's drag&drop facility to copy pictures from the card to the computer's hard drive, the same way you copy any other files. Or you an use iPhoto or any other photo cataloging program.