Hello All, I have run into a crazy situation when replacing the HDD in a MacBook Pro. I upgraded Yosemite on the old HDD. Then I powered the machine down, took out the old HDD and installed the new HDD. I plugged the old HDD into a USB adapter and powered on the MacBook while holding the Option Key. The old drive did not show up as a bootable option. I installed Yosemite from a USB drive on the new HDD and was simply going to use Back to my Mac. But it also could not see the old HDD. So I created a user account and logged in. Once inside I got a message. "The Disk you inserted was not readable by this computer." Referring to the Old HDD plugged in via USB. Fearing the worst I powered down, switched the HDDs back and booted to the old HDD again. It booted without and issue. I tried plugging the new drive in via USB and got the same message... "The Disk you inserted was not readable by this computer." I am losing my mind trying to figure this out. Has anyone else encountered this issue? How can I get the data transferred. Thank you for any help!