You do need to do chkdsk like he said, but I would hold off for a moment. chkdsk will attempt to repair the file system, even if it has to destroy your file to do it, so I might try a couple of gentler options first.
Mount it up on a Linux computer if you (or a buddy) have one, and try to copy it off onto the linux computer. I have saved a lot of data from funky drives using Linux. It won't recover a bad sector automatically, but it might just read the whole file, including the bad spot, without freaking out like Windows tends to.
If the recording is an important one, I would try to do a transfer by patching the output of the iRiver into something else and playing it back (digi to another iRiver is ideal, but even analog into your computer's sound card line it is better than nothing).
Then run chkdsk like he said. I generally run "chkdsk /f x:" for "fix" first, try to recover the file, and then run "chkdsk /r x:" for "recover" second.
Good luck.