Canon EOS 1D Software Instruction Manual page 222

Troubleshooting
When the "Communication between the camera and computer failed" or "Software not running
correctly" message appears, check the items described below.
I have installed the software but the camera and
computer cannot communicate.
Does your computer comply with these requirements?
A Macintosh with a FireWire (IEEE1394) connector as a standard feature.
* Operation is not guaranteed when the camera is connected to a FireWire (IEEE1394)
interface that is not a standard feature of Macintosh.
Are the camera and computer connected correctly?
Connect the camera to your computer correctly using the dedicated cable (M-8).
Is there sufficient charge left in the camera battery?
Your computer does not supply power to the camera. Connect the DC Coupler Kit to the
camera or load a fully charged battery into the camera before connecting it to your
computer.
Do you have more than one camera connected to your computer?
If you connect more than one camera to the same computer, the driver and camera may not
operate normally.
Quit the software and disconnect all the dedicated cables. Then connect only one
camera to the same computer again.
M-98