I have a PCI eSATA raid controller in my classic Mac Pro '09 running El Capitan which I am using in JBOD mode with an external 4 drive enclosure and also for a OS 10.8.5 external boot drive for running some essential legacy software. In El Capitan I keep getting this error even though I have neither ejected nor turned off the Mt. Lion boot drive (in OWC single drive enclosure): Disk Not Ejected Properly - Eject "Mountain Lion" before disconnecting or turning it off The same drive, when booted from, locks up while using unless disk sleep is disabled. The card requires a driver which is installed, configured and works with no problems for all but the Mountain Lion disk. I'm guessing this is a card driver problem but I don't understand why it should be precipitated by sleeping the drive. Wouldn't the driver be loaded at boot time and remain in memory? Any ideas as to how I can troubleshoot?