Just to confirm that I've struck similar issues (with various commands) over the years, and the first suggestion that haukex
mentioned has worked, for reasons that I've never worked out.
I think the problem is that either the source file or the destination (probably the latter) is not being found.
If the scp executable was not being found you should instead get the following error:
'C:/Windows/System32/OpenSSH/scp' is not recognized as an internal or
+external command, operable program or batch file.