File.chmod will presumably only work if your Ruby process is being executed by a user with the required permissions to run chmod in the first place; I suspect not in this case. Change the permissions on the directory with your files in so that user can access it, using the shell.
didn’t realize you were on a windows box - life can be somewhat less rational there. unix has used the same permissions model and change commands since it’s inception in 1970. calcs showed up sometime around windows2000/xp and has now been depricated for use on windows7.
you could save yourself much heartache (measured in decades) and build yourself a linux box. microsoft does not make a software development environment, they only make money.