Marfitalu: It seems that rewritable CD´s you have bought are not compatible with your writer.

If possible, try to exchange it by another types of CD in shop you bought previous ones.

What kind of CD driver do you have?
It can be that you bought faulty or defective CD´s . Try to find some app using to find out all infos about your CD´s for example in www.cdmediaworld.com. Maybe that can help.