From the Nero site - Power calibration error can be cured / caused by
* Update the firmware of your recorder. Please check the manufacturer's website for the latest version.
* Try another brand of CD-R or CD-RW media.
* Try different power connectors, and for recorders, do not share power with other devices. It needs its own power connector. If the error occurs with an external recorder, the power source in the chassis could be the cause. As a test, try to take the recorder out of the external chassis and connect it internal.
* Try different configurations, such as taking the CD-ROM to the primary IDE bus as slave and have only the recorder connected to the secondary IDE bus as master.
* Send the recorder in for service.
Also can be caused by dust on the lens