A baffling aspect of iTunes/iPod is the inability to copy mp3's back from the iPod to your pc. Data transfer is strictly one-way.
I spent a lot of time trying to find an app that would do this simple task, and finally bought one. It failed; I got "Error:The parameter is incorrect," and most files failed to copy. I contacted their technical help, and it didn't. (Help, that is.)
Then a coworker recently pointed me to Sharepod. It's a very simple bit of freeware, and I gave it a try.
Initially, it gave the same error. So I checked Sharepod's Help page, and it suggested a repair on my iPod, as if it were a disk drive. I did it, then all the files copied like a charm.
And now... you know that.