Chimera boot0 errors

I have boot0 errors when trying to boot with Chimera, the same as per the below

http://www.tonymacx86.com/25-boot0-error-official-guide.html

However when I try to follow the first method, I can't unmount the drive even if I use the terminal instructions here,

http://www.tonymacx86.com/yosemite-desktop-support/143781-boot0-error-after-multibeast-chimera-install-yosemite.html#post888730

I get a failed to unmount. Any idea how to fix?

Thanks,

submitted by YuntiMcGunti

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