Once, this happens to me as well. and when I googled the matter, I got to know that this happens when the permissions on the file is wrongfully set to 000 (which means that no one can read, write, or execute that file). Then I just changed my file permission privilege into Read & Write and it's worked for me.
To change file permission settings on mac: Right click on the particular file and click on Get info from dropdown menu and refer to the sharing and permissions panel and change privilege settings into Read & Write