iPhone 5 refusing to sync because not enough space even though there is

Hi guys,

I've had this problem for a few weeks now. My iPhone 5 refuses to sync when plugged into my laptop because it says there isn't enough space. It usually says I need an extra 8-9GB. The bar at the bottom shows that I'm not even using all the memory on my phone, and I'm not trying to install anything that is big enough to require an extra 8 or 9GB above what is already free.

Does anyone have any tips on how to deal this and resolve the problem?

Thanks.

I'm attaching a screenshot of the error message, and of the bar so you can see it's not full.