I am trying to set up an external hard drive with a copy of Windows 10 that I can boot from my MacBook Pro (Early 2015). I used the procedure posted by Alex Lambert in the following thread:
Following his procedure, I never received any error messages, but when I reboot my MacBook and hold down the option key, the only bootable hard drive listed is my "Macintosh HD". If I open System preferences-->Startup Disk, it finds my external hard drive as a Windows disk, but if I try to select it, then I get the error: "You can't change the startup disk to the selected disk. The bless tool was unable to set the current boot disk."
How can I check what is missing on the hard drive that keeps it from showing up in the startup disk selection?