Jailbroken ipod wont copy music to itunes

Hello, I recently jailbroke my Ipod 4g and everything went fine. I downloaded this thing from cydia where you could get music for free. It advised me to plug my ipod in and configure it so i could manage my music manually from my ipod. Now, i am trying to unjailbreak it. But i have encountered a problem. It wont sync my music from my ipod to my computer. Not the muysic i downloaded from the app, but music i downloaded legally from itunes. It says that sync music is deselected, but when i select it, it tells me it will delete all my legally downloadeds music and replace it with what is on my itunes account. If i deselect manually manage my music, it tells me the same thing! Help!