ITunes items not transferring to IPhone?

[brenda]

I wanted to do an update on my IPhone, so I connected it to my computer and synced it. It looks like it's backed up just about everything. When I click 'Update' in ITunes it comes up with a box that says 'There are purchased items on the IPhone that have not been transferred to your ITunes library. You should transfer these items to your ITunes library before updating this iPhone.' I have tried everything I can think of to transfer them, but no luck. Anybody know how to do this or have this problem as well???
It's not jailbroken