How can I get camera and laptop to communicate?

SOURCE: Camera not communicating with new computer

I think that Canon has an update, there are differences between Panther (10.3) and Leopard (10.5) Check here at CanonUSA

SOURCE: camera wont transfer images to laptop

If the camera displays "Communication Error," when trying to download images the main cause for this error is that there are more than 1000 images stored on the memory card. It is recommended if there are more than 1000 images on the memory card, that you use a card reader to acquire the images, or to delete images off of the memory so that there are less than 1000 images to download from the memory card.
If this is not the case, there are not 1000 or more images on the memory card, try reconnecting the camera to abnother port on the computer, try another cable or another computer. This error can also display when connecting to a direct print printer. Please check with the printer manufacturer for more information on this error.

SOURCE: Urgent: Communication Error- Camera Not Detected

I have the same problem but I just changed the SD Card inside with another SD Card (non SD HC) and the communication problem went away.

SOURCE: i am trying to download pic, communication error on camera

Not knowing your computer OS hard to say. Try re-installing the camera software.

SOURCE: Communication Error on the camera screen?

Time to start using a card reader.