I don't know whether you're using BearShare or LimeWire since you originally posted in the BearShare forum section. But ... use some of the tips here How to transfer music to my iPod (& iTunes). I always recommend the Manual Updating of the iPod. And make sure your iPod is not full. The Shuffle doesn't hold a lot of songs, depending on which model you have.

Sometimes you need to reset the iPod. That can be a nuisance because you lose all the songs on the iPod. Are you sure you have all the updates for your Shuffle. If you're using the latest iTunes then you may need to update the shuffle also. You can find links to updates & other issues here http://www.apple.com/support/ipod/