My imac last nite kept ejecting my usb stick even though was copying data from stick to mac. Used this stick many times and it works fine in my 2012 macbook pro. It is being plugged into a usb 3.0 powered hub (yes i know the imac only usb 2.0). there is a time machine 2.5" HDD connected to the hub which does not eject. the mac is set to never turn off hard disks. the time machine was and still is working fine. I tried stick in the keyboard but mac claimed not enough power to drive the device. the stick was ejected giving the error, please eject before removing the drive. I did not remove the drive. 7 port hub, tried 4 of the ports before giving up as was getting late. Will disconnect the cinema screen hub and the 7 port hub and try direct to mac. But it has always worked like this in past, as stick works in macbook pro then it would seem the hub is cause?