Hi, Today I installed an AccelsiorM PCIe card with a Samsung EVO mSATA SSD in my Mac Pro 3.1. I then booted the computer using my current boot drive (OS X 10.10.5) and since I saw that the SSD was recognised, I proceeded to install El Capitan on it. In the middle on installation, the Mac rebooted, but instead of booting El Capitan, it booted from a 10.6.8 partition ! I rebooted the computer and selected the SSD at boot time (using the option key) and installation of El Capitan completed without issue. Now, when I reboot the computer and hold the option key, I can choose whatever OS (10.6.8 or 10.10.5 from SATA hard disks, or 10.11 from the SSD), it boots and works correctly, and all other OS partitions are mounted and usable. But whatever the selection in the Startup disk preferences, the computer always boot 10.6.8 by default ! In 10.6.8 I only see the 10.6.8 disk in the Startup disk preferences. If I use systemsetup setstartupdisk to set another disk, I get errors that /Volumes/THEDISK/System/Library/CoreServices is not a valid system (where THEDISK is either the 10.10.5 or 10.11 partition) From 10.11 and 10.10.5 I see all bootable partitions in the Startup disk preferences, if I choose e.g. 10.10.5 while booted in 10.11, the computer will correctly boot 10.10.5. But if I choose 10.11 from either 10.11 or 10.0.5, the computer reboots in 10.6.8. If I then reboot and use the option key to boot 10.11 and open the Startup disk preferences, it tells me that 10.11 is the selected boot disk. In 10.6.8 I see that no boot disk is selected in Startup disk preferences (nothing is written to the left of the Restart button). If I use systemsetup getstartupdisk the answer is /Volumes/SSD/WINNT (!!!) SSD is indeed the name of my 10.11 partition, but I have no idea where WINNT comes from !!! Of course this directory does not exists. The expected answer would be /Volumes/SSD/System/Library/CoreServices… I’ve reset the PRAM but that didn’t change anything. Any idea what’s going on and how to fix it ? Thanks a lot for any help ! EDIT: I forgot to mention that the SSD disk is seen as removable by the OS, though I'm not sure if this is relevant.