There are two common causes for power calibration errors.
Low Quality Media
At the start of each burn the drive will burn to a small section the the disc to adjust the laser power for the media being used. Low quality media is inconsistent and will frequently give hit or miss results during the power calibration. AN32, CMC and Moser Baer are common low quality media.
Keep in mind that many of the brands of media aren't actually made by the company selling them. To find out who actually manufactured the media you can use DVD Identifier.
Some of the best makes of media to try are Ritek G04/G05, Verbatim Metal AZO, Maxell and Taiyo Yuden.
The only recourse for power calibration errors with low quality media is to update the firmware for your drive and hope it works. Here's a link to the best firmware page to be found:
If you've never flashed a drive before I highly suggest checking out the forums there and read up on the process before attemting anything.
Your Burner Is Dying
This one is self-explanatory.
If you're using quality media, your firmware is up to date and you're still recieving power calibration errors then your old drive is dying or your new drive is most likely defective.
If problem in Nero then:
1 on desktop click start
2 select control panel
3 click on administrative tools
4 click on services
5 browse your way down to IMAPI CD BURNING COM SERVICE
6 right click (on IMAPI) then select properties
7 in the middle of the window it will say start up type.click on the arrow to the right and select disabled.
8 make sure you click APPLY
you should notice that Nero starts alot faster aswell.