I recently found my system crashing after about an hour, this would happen without doing anything in particular.
I did some investigation, cleaned up drives, etc, then found out it was my 512GB SSD that I bought over two years ago - it needed a firmware upgrade.
So I followed the information in the above link, only to find it didn't work for the mac.
After a lot of hunting I found this article which pointed to this older article that wasn't needing translation.
I followed the tutorial, and took the advice to section off a bit of my extra hard drive (the non SSD 750GB drive in the DVD Rom enclosure), and tried to boot off it - it wouldn't boot.
So now that I had the correct disk image copied from my flash rom drive on a 5GB partition on my 750GB drive, I found I needed to download the newer rEFIND Boot Manager , specifically the USB flash drive image file, and followed the instructions to install it on the 16GB Flash ROM drive.
I plugged the 16GB Flash ROM drive in, restarted while holding down the option key, and it asked me to select my usual options but also a orange drive that was the rEFIND Boot Manager that was on the Flash ROM Drive. Once selected it asked me if I wanted to use the SYSLINUX partition that I had made by following the article above. From there I followed the instructions to install the firmware upgrade.
I hope this helps someone!