I was using a MBP 2012 10.11 and I've been writing files to an external 128GB MicroSD with Built-in card slot. I've moved to a MBPr 2013 10.11 and the same card cannot be written to. Works: 1. 64GB Exfat Card with Built-in slot 2. 128GB Exfat Card with external card reader 3. 128GB Exfat Card in Parellel Not Working: 1. 128GB Exfat with Built-in slot I am lost, I don't know how to fix it.