I stupidly deleted many old back-up off of my external harddrive. Noe Time Machine can't do a backup because it says it has 515GB of data and I only have 499 GB of space. My data was never this large before I deleted the files. When I open About This Mac it says my space used is only 401GB on the internal harddrive. Something happened when I deleted the external harddrive files. I have erased everything off of my external harddrive and now I can't even do one backup. Help!! I called Apple support but they really aren't sure how to fix the problem.