I bought two SanDisk 16gb to make two backups for my imac. The first one went fine and I unplugged it I got an error message that the disk was not removed properly, which I ignored. I plugged in the second Sandisk and tried to make an identical backup, but kept getting the “error code 43” message. I plugged the first one in to make certain my backups were there, and they were fine. Before I unplugged it, I right clicked and clicked on “Eject Disk”. When I plugged the second one in and tried a backup again, it worked just fine.