When a CDRW has been burned/written to and finalized, it technically becomes a CD. No longer a RW.
In order to use it again, it needs to be blanked first. You can do this with cdrecord, and, if you like, you can blank and burn in one command. To blank, do like this:
cdrecord dev=0,0,0 speed=10 blank=fast padsize=63s -pad -dao -v -eject
That will blank a CDRW and make it ready for use.
to burn and blank at the same time, use something like:
cdrecord dev=/dev/hdb speed=4 blank=fast padsize=63s -pad -dao -v -eject /absolute/path/to/image.iso
and to simply burn, use:
cdrecord dev=/dev/hdb speed=4 padsize=63s -pad -dao -v -eject /absolute/path/to/image.iso
I use the dev=/dev/hdd instead of the SCSI way of 0,0,0. This works only with a 2.6 kernel as far as I know.
I'm not sure if the 'speed' argument affects the 'blank speed', so I prefer to blank and burn in separate steps, though I have had success both ways.
You need to use the PAD option if you want the disk to work properly, especially if it will be used on a CD drive other than the one it was made on.