Extracting Data from Corrupt/Unreadable CD

[vee_ess]

In attempting to back up about 800-900 MB's of files (many of the large files were compressed), I started to burn the files to CD. Sometime during the process, an error occured and now the CD has become unreadable by normal means. Since the CD uses the Joliet filing system, I know that it is possible to recover the files on the previous sessions. The problem is that I can't find any [free] software to do it. Please tell me if you know of any free titles I can use. Thanks!