I give up!! - Terminal error; "/Volumes/MyVolume is not a valid volume mount point" -- HELP!!

I give up!! - I've followed the instructions (to the letter!) for every version of the OSX installers - and ALL are working fine, EXCEPT for SIERRA!! -- Every troubleshooting attempt I can think of results in the same Terminal error; "/Volumes/MyVolume is not a valid volume mount point" -- HELP!!

Before you ask, YES - I have named my destination drive "MyVolume" - and YES, I know it is case sensitive...

I've wasted too much time researching this -- and I know there are a ton of others having the same issue - but no resolution so far...

anyone??