Problems with transferring purchases...

When I sync my ipod to itunes and want to sync new music on it, it starts the process like usual like backing it up and then when it gets to transferring purchases from ipod it doesnt load it just stops, and its on the apps. it will say "loading 1 of 8: Facebook (or whatever app it needs to transfer thats on my ipod but not on itunes) but it will never finish loading, thus i cant load my songs i want on my ipod. what can i do to fix this? thanks