Check the front 4 drawers to see that all 4 have a bright blue light. Shut the unit down, remove the drawer for the drive reporting the error. Check for any obstruction or issue, then reseat the drawer back into the slot and restart the machine. If you still have an error, contact tech support to arrange an RMA if the drive is still under the 3 year warranty. If out of warranty, the drive itself may still be returnable to the manufacturer depending on the model.