Power calibration is a thing that an RW drive does to adjust the power of the laser based on the type of media in the drive ..
The simplest way to avoid this problem is to change the media .. try diff. brands of cd's ..
Another way would be .. to uncheck the smartburn feature in Nero .. This will stop it from checking the media type .. U can also reduce the speed ur burning at ..
The higher the speed ..the more power the laser is set at .