No longer able to move install folder on Steam?

[worldofneil]

all SteamMover really did was copy and paste the files over.

That's actually all there is to do to move a game on Steam from one library to another.

Create the library first in Steam (if it doesn't already exist)
Exit Steam
Move files on disk
Move the appmanifest_39210.acf file as well (this is the ID file for this game)
Restart Steam

When you load Steam it scans all libraries for the ACF files, as long as you moved that with the actual files, you're done