From Nero website:
http://ww2.nero.com/enu/FAQs_Products_NeroBurningROM_Error-Messages.html#9
Quote:
9. I get a 'Power calibration error' or 'Calibration area (almost) full' error message. Why?
Power Calibration is controlled by the recorder.
Before any write operation, all recorders must do a 15 step power test to determine the optimum power for writing to the CD; this is called "Optimum Power Calibration"(OPC). During the write, it continues to do this test to get the best write throughout the whole CD; this is called "Running Optimum Power Calibration" (ROPC).
This whole process is controlled by the recorder, though initiated by programs such as Nero. There is an area on the inner part of the CD for the test and test data info to be stored. You can use this area up to 999 times.
If you receive the "Power calibration error" or "Power calibration area is (amost) full" error message, the cause will be either poor media, poor power, or a defective recorder.
Please try the following solutions:
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.