Installation Failed unable to mount boot partition.

Down loaded Dmg. Followed instructions to drag to application folder. Open dmg after placing it in application folder. From the application folder. Selected my flash drive as the choice available. It ran its install and told me it was safe to eject my flash drive. Took flash drive put it in AppleTV(silver). “FC” appeared and it install for a 10sec then said “Installation Failed Unable to mount boot partition”

Any help would be appreciated.