The default syntax of robocopy takes folders as parameters and copies source folder to destination. To copy a file, the syntax is the following:
robocopy C:\source C:\destination filename.ext
Notice that filename is not part of the source here. Also, because of this limitation a file can not be copied to another location with a different name. Due to this, in msbuild projects, you need to copy the file using robocopy (assuming you use robocopy) and then rename it.