Sudden 'Power Calibration errors'

Hi everyone,
about 2 months ago, i bought a Aopen CD-rw. It was working fine until, from one day to another, it started refusing burning cds and stating a “Power Calibration error”.
There had been NO software changes, nor firmware actualizations or hardware related issues.
It started with the same media brand that I always used with it (verbatim, (bulk/spindle) ) and I also tried jewel case verbatims, Imation, HP, and an unbranded one.

The crazy part is that, later n, I found that I was alble to burn in higher, yes higher, speeds. I burn data backups, so for the sake of data integrity, I alway use the CD-RW at its lowest speed (4x)

I took it to the vendor, but he is a little reluctant to change the unit,and says that I should try a newest version of Nero or a different program, even when he inadvertly murmured having some troubles with Nero.
the point is that I need a CD-RW that I can trust, and if nothing changed in my system, why would the unit fail unless there is something wrong with it?

Please, can anyone tell me what could cause this power calibration error? And what could have caused it?
Thanks a lot !

try this thread

http://club.cdfreaks.com/showthread.php?s=&threadid=46699&highlight=power+calibration+error