[X4U] laser can't calibrate for media

[nk]

I have 2 mac minis, one of which can burn DVD-R, the other can't. I 
bought them within 2 months of each other, and they're same speed, same 
config, etc.

both have same model SuperDrive, and in System Profiler, both say they 
can burn -R

Yet one of them "can't calibrate laser to the media" according to a 
warning I get when attempting to burn.

Is there something I can do or run or install to "make" that Mini 
calibrate its laser properly for -R media?

thanks!

nk