Not Enough Space to Sync

I would like to sync my iMac iTunes library with my iPad. I deleted my entire iTunes library from my iPad, closed the iTunes app, and restarted the iPad. I connected it to my iMac, opened iTunes, and selected the "sync music" checkbox for my entire music library which resides on my iMac. The graphic storage indicator at the bottom of the iTunes window acknowledged the additional audio data to be synced and still showed an additional 13 GB of free space. When I click sync I get an error message that there isn't enough storage and the sync is cancelled. If the graphic indicator shows that there is still plenty of free space after I add my library, why would it then tell me that I don't have enough space?