Check that the white calibration tile is clean and free of debris. If you have more than one i1Pro, verify that the serial number on the calibration base matches the serial number of your unit.
i1Pros pull a great deal of power from the USB port. In some cases low or intermittent power from the USB can cause a calibration failure. If you are using a desktop computer be sure that you are using the USB ports on the back. You can also try using a powered USB hub to improve the supply of power to the i1Pro.
We recommend to use the original USB cable. If you use another, it may be that it has a different resistance and delivers too little power to the i1Pro spectrophotometer.