Not enough disk space problem!, Not enough disk space problem!

Hey Guys, how come when I try to download additional content it says I have to delete unnecessary files because I don't have enough disk space although I have 10 gb of disk space left, the additional content total is 6.8 gb. Something also does not make sense because the additional voices loops I want to download takes up 907 mb, (says this on the right of page) but at the end the total is as stated 6.8 gb.

Really Urgent, Please Reply!!!!!!!!