So I've been having this issue for quite some time now.  Anytime I have to reboot my server, if I don't move the Pro.key file to or from the config folder it doesn't boot. Instead it sits on a "loading operating system" message. Once I move it though, it boots fine and normally.  I am using a Gigabyte MA74GM-S2 motherboard with my boot settings set to boot only on the USB drive.  I am also running 4.7. It's been this way since 4.5 I think. I've done everything to make my USB drive bootable too and that hasn't done anything.  It hasn't really been a big deal because I rarely reboot but it is getting a little annoying and I've looked EVERYWHERE on the forums to try and fix this and there hasn't been any topics on moving a key file before it will reboot.  

 

Hope you can help. Thanks.      

I'd be suspicious of the fat's integrity. Have you chkdsk'd the flash drive?

I just ran a chkdsk on it and it passed with flying colors.

Ok I just figured out that the key file doesn't have anything to do with it.  I first realized if I just plug my flash drive into another computer and then back into my server it boots fine without moving any files. Then I tried just removing the flash drive from the server after it has shutdown and plugging it right back in and oddly enough it boots correctly. I also tried flipping the switch on the PSU after shutting down to off then back on and rebooting and that seems to be working too.  So maybe the flash drive has to lose all power first before it can boot again correctly At least I know now that I don't have to plug it into another computer and swap a file around.  It must just be this samsung flash drive. I guess if it keeps bothering me I'll just try a new one then.

Could it be the BIOS settings for USB devices?  Either the Boot settings that detemine what type of USB device the motherboard thinks is plugged in, or settings related to USB storage?

I've already tried all of the usb settings.  My mobo gives the option of usb-hdd, usb-fdd, and usb-zip. All of which boot the same to boot unraid. I also have my boot priorities all set to boot from usb.