OPA is operating under Admin mode. If you want to migrate a folder from a network drive, you need to map the network drive in an admin mode CMD.
Run CMD.EXE "as administrator" (Push windows key, find CMD / Command Prompt. Right-click on it and select "Run as administrator")
In admin command prompt map network drive using the "net use" command :
net use DRIVE: PATH
net use s: \\tower\movies