I just went to sync my iPhone and I was given this message. This ‘lack of space’ is not a lack of space in your computer, the ‘lack of space’ is on the iPhone. This is somewhat of a bug. I think it is because iTunes is wanting to do some updates to the iPhone and there’s not enough room on the iPhone for this to happen. Whatever the cause, the solution is quite easy. Just uninstall some stuff from your iPhone (e.g. movies, music or photos), sync it, then put the stuff back on. Here’s how.
That will probably do the job but if your phone still won’t synchronise you might want to remove some music.
2. To delete music, just go into iTunes, and unselect ‘Entire music Library’.
Below that you can select or unselect individual songs and albums to remove them from the iPhone.
If your iPhone still will not sync, you might have to remove some more ‘stuff’.
3. In iTunes you can go through the various tabs for audiobooks, movies and TV shows and unselect more items.
Eventually you will get to a point where your iPhone will sync successfully without the error message. After that you can load your iPhone up again with your photos and music if you want to.