I see, it seems that the tool isn't finding the "xcopy" program for some reason.
I have opened an issue on the repository so I can take a look at it later:
https://github.com/haroldo-ok/BlocklyVN8bit/issues/54
Maybe this workaround could fix it until then:
https://stackoverflow.com/questions/25500650/batch-file-error-xcopy-is-not-recog...