I had 210.81GB available on my hard drive. My external Time Machine backup refused to copy over my iTunes folder, whether it was through Time Machine or direct copy. My iTunes library is 174.73GB so it should fit fine, but apparently it was giving me this error for no reason! My Time Machine drive is a FW800 drive partitioned for 2.5TB of backup and 0.5TB of personal use. I thought it was because the current iTunes library was taking up too much space, so I'm deleted that. Disk is very healthy, Momentus XT on SD28. It still gave this error. Then I disabled the Time Machine local snapshots through: and it instantly freed about 140GB of space from my internal drive. After that, the copy went fine.