Yea I think your boot partition isn't correctly set. Try this: when installing yosemite, format your hard drive. Do a 1 partition scheme and set it to master boot record (mbr). Then format again to the GUID table. That fixed this issue for me.
I was having this issue and managed to solve it with a simple fix.
I realized I incorrectly set up my unibeast flash drive. When I erased the drive, I used disk utlility to do a simple format. Instead, do a 1 partition with master boot record selected. After that, I think I did another...
I finally got it working on this motherboard, and it turned out to be easier than previously thought. I'll go through the mistakes I had and then how I got it working.
At first, I had errors galore. Couldnt find mach_kernel (even on unibeast 5.0.1), had issues with reboot...