Suddenly my Macbook is not copying files to my external drive or USB sticks anymore. It worked fine before and when I plugged the external drive in TimeMachine backed up as usual. But now when I try to copy larger files (small files seem to work fine, say anything under 1GB) to a USB stick, or even between the two partitions of my external drive, Finder shows me the copying window, establishing a time remaining. It then copies as usual, but all of a sudden the Finder window disappears and when I click on Finder again my file "seems" to have been copied, but is transparent in the location it should have been copied to and can't be opened. I already verified and repaired disk permissions and I have no other idea what to do. My USB stick is formated as FAT32, so is one of the partitions of the external drive. The other is OS Extended. Can someone please help me?