Not enough free space available to sync (but can't remove anything!)

This afternoon I attempted to sync my iPhone to my Windows computer, but it came up with the message, "The iPhone _____ cannot be synced because there is not enough free space to hold all of the selected items (additional 607.3MB required). I have noticed that my storage had been getting a little full so I deleted a couple of videos so it would free up the extra space. However, that wasn't enough and even after "removing" my music library (and freeing up roughly 23GB) I still am told that there is not enough space on the iPhone.

I have checked the iPhone directly and I've found that all of my music and videos etc have remained and I cannot delete them. I have tried deleting them both in the corresponding app and through Settings, but nothing works. I have even tried restoring it but iTunes tells me that an error occurred so that isn't working either.

I would really appreciate some advice.

Thanks in advance.