This is driving me mad. I have a late 2012 iMac 27" running 10.10.3 and a Sandisk UltraII mounted in a Dynamode 2.5" USB3 carrier formatted for MAC OS Extended (Journaled). It works perfectly if I plug into the left hand end of the wired keyboard but is not recognised if I plug into the USB ports on the back of the iMac. I have tried turning off - removing power lead and restarting then plugging all the USBs back in but its still not recognised or even visible. Suggestions please.