More information please. Syncing between what devices - two iOS devices, or your iPad and your computer?
If it's your iPad and computer, I'll preemptively say that you probably upgraded your iPad to iOS 8 and chose to upgrade to iCloud Drive, as well. If so, you'll either need to install the OS X 10.10 beta, or wait until OS X 10.10 is officially released. OS X 10.9 has support for iCloud, but not iCloud Drive (which is replacing standard iCloud).