Could you please check if full permission is given for the user to both the source & target paths?
What I find puzzling is that I've seen UNC paths ( \\dir\filename) only in conjunction with Windows systems, but - according to the cp command - to me it looks as if you're working on Linux or Unix. And under Unix/Linux directory paths usually point to some mount points within the directory tree, no UNC paths involved.
One hint to a potential problem here is the message in the session log "the system cannot find the path specified". Can you please try to use a "normal" directory path instead of the UNC path?
As for the FTP server, either you can access that path within the directory tree (via some mount point) or you will have to issue some "ftp" command to transfer the file to the FTP server; I don't see any other way to achieve this.