The iPod cannot be synced the required file is locked.

Hey,
I used to do this regularly but today when I try to synchronize with laptop it throws me an error. I am not able to download new songs to my iPod because of this error. I am not hardware tech person so finding very difficult to resolve this error. I tried it again by rebooting the laptop and iPod but the error remains the same. Please help me to fix the error. Thanks a lot.

ITunes
The iPod cannot be synced. The required file is locked.
