I have experienced this myself. A friend had this happen to them and the nice folks at the Genius Bar at the Apple Store relayed this information to them...
If you leave your iPod plugged in for a long time, or don't charge it for a long time, this can cause power memory issues with the iPod. Basically the iPod gets frozen into thinking it does not need charging and so it does not hold a charge.
It may look like it is charged but actually it is not. This is "supposedly" not fixable and they will suggest you give up your iPod and purchase a refurbished one at a cost that is much less than a new one. (My guess is they take your iPod and fix it and then sell it to the next customer as a refurbished iPod.)
You have your iPod loaded with your songs for your party. And now you want to be sure the iPod is charged up, so you plug it in a week before the party and don't touch it.
Be aware this can cause a problem.
Just Press Play Productions