Recovering data from a flash card is a problem that happens often enough that the manufacturers of the flash cards give away software to address the issue. Use Google to search for "xxx data recovery" where "xxx" is the name of the flash card manufacturer (Lexar, Sandisk, Kingston, etc.) .
If the manufacturer's free software doesn't do the trick, you might try other free software, such as
http://www.z-a-recovery.com/digital-image-recovery.htmhttp://www.aumha.org/a/recover.phphttp://www.pcinspector.de/smart_media_recovery/uk/welcome.htmIf these programs don't work, you might purchase a data recovery program like Photo Rescue, $29.
http://www.datarescue.com/photorescue/index.htmAnother inexpensive program is Recover Lost Data from Stompsoft, $39
http://www.stompsoft.com/recoverlostdata.htmlAll these programs are for the PC. I'm sure a Mac user can contribute links to similar programs for the Mac.
And if you still can't recover the files, then consider employing the services of a data recovery company. They have proprietary tools that can access the card independent of the operating system, and usually recover data that can't be reached by other means. These services don't come cheap, but compared to losing the original recording, they can be a bargain. I paid a company to recover 750 MB of recordings made in Venezuela, for example. The cost of the company's services were a lot cheaper than flying back to South America to re-create the original recordings.
Flintstone