CD-R vs. CD-RW...why won't the latter work?

[<jbmaxson@surfglobal.net>]

Hey ya'll,

got myself a cd-RW writer the other day and a pack apiece of CD-R's and CD-RW's.  I package
up a nice little .iso of my home directory with this line in my crontab:

    00    5     *        *       *     mkisofs -R -o /tmp/image.iso /home/jbmaxson

and it daily (at 5:00 am) pukes out an image just as I'd like.  Now, I'd like to follow that
up in the crontab with a command to burn that dude to a CD-RW so that I can get a daily backup
of my directory...I'd like to use something like the following:

 cdrecord -v dev=0,0,0 speed=4 blank=fast driveropts=burnfree -data /tmp/image.iso

Seems to me it should work.  All systems seem nominal during the burn, but when I go to mount
it with "mount /usbcd" it gives me the error

mount: wrong fs type, bad option, bad superblock on /dev/scd0,
       or too many mounted file systems

however, using the same image, I can burn a normal CD-R (not RW) that mounts just fine.  The
command I've used for that burn is (if I remember right)

cdrecord -v dev=0,0,0 speed=4 driveropts=burnfree -data /tmp/image.iso

Is there anything I'm missing in the man-page for CD-RW's that I didn't consider?

thanks,
Jeff