Apparently there are 2 types of CDRW discs. The originals and the newer higher speeds.
My first CDRW's are unformattable/unwriteable with my newish CD burner, but still work fine in my original 2x.
So, if you have a lot of older CDRW's around, you may want to hang on to your old CD-burner too!
Just an FYI!