I recently took one of my re-recordable CD's and tried to burn a new
folder of graphics onto it (I am a professional digital photographer).
 The CD had some VERY important files on it, and, as I have often
successfully done in the past on my PC, I tried to add the new folder
of graphic/picture files onto the remaining ample space that the CD
contained.  However, this time, using my Roxio "Easy CD Creator"
software, I inserted the CD AFTER I had already set up the folder to
be burned in the Roxio program, and I didn't see the mirroring phase
take place that usually happens before I can tell the program to go
ahead and create the CD (i.e., I didn't see the folders that had
already been burned to that disk appear as grey folders in the Roxio
window on my desktop prior to the final burning phase) but instead, I
saw a narrow window appear that read:  "Would you like to add another
volume to the disk?"  Of course, since that was precisely what I
wanted to do, I hit the "YES" button, and the program burned the new
folder of picture files onto my RW disk--and, as I later discovered to
my horror--seems to have erased, or at least obscured/rendered
unreadable ALL of the OTHER files that I had previously burned onto
that CD!  What happened???  Have I forever lost all of those files? 
Is there ANY way that they can be recovered; are they "hiding" there,
on my CD, in some other form, that can somehow be accessed perhaps
with some additional software recovery program, such as I've read is
available when something has been erased from a hard drive disk? 
There were some extremely important images that I had burned onto that
disk, and if there is any way possible that I can recover them, I
certainly will take great pains to do so.

Hi,

First of all, don't worry. You cannot destroy the data on a CD-RW
permanently unless you format it. Adding new sessions only change the
"visible" file list.

I'm not an Easy CD Creator myself, but you can try the following: 

First, copy all the files you can normally access on the CD to a safe
place.

Then, put the CD-RW into your CD recorder and using Easy CD Creator,
select "Import Session". You should now see two (at least) sessions in
the list. Select the previous session (not the latest one) and try to
import.

If you can import it, try re-burning the CD without adding any files.
If it does not allow you to burn without adding new files, add some
dummy files and retry.

If all goes successfully, 

Let's see if it works.

Regards
Bio
Google Answers Researcher

If there was some error writing the TOC to the disk or a similar
failure, a disk recovery utility like spinrite 5 available from
www.grc.com will open up all the data recorded on the disk, including
any recoverable damaged data or data without a working file table.