Thank you Michael for the feedback. I did the backup... when I picked them up and saw that that shinny label surface had turned into a strange brownish yellow. I thought I would not be able to recover the data, but strangely enought the cd-r still works. The process didn't stop... it is still getting darker.
To tell the truth, I never lost a CD-R in my life. I've been burning them since 2000: TDK, HP, SONY and EMTEC. Recently the TAIWAN HP and EMTEC VIDEOLAR made brazilian CD'Rs.
The only 2 CDs I lost were not CD-Rs. They were regular music CD's done by normal Record Companies (Polygram):
One was IT'S BETTER TO TRAVEL by SWING OUT SISTER. But this one was really abused: after 10 years of heavy use it stayed in a country house in the open air in the rain, in the hot sun, it had deep scratches on the label surface, it was dropped in the pool full of chlorine: no one saw and it stayed there for 3 days.... As expected, in a process of months the shinny label side became transparent, full of thousands of little holes the size of a pinhead... as if it was dissapearing away.
The other one was also a regular professional music CD done by EMI or whatever... it was KING CRIMSON's THRAK. It was also abused. It stayed in the open air for a long time in that country house, in the night cold moisture. A kind of fungus grew inside the disk and the music went away.
I replaced those 2 and today I treat the CDs and CDRs with much care as I can.