Theme Editor changes Won’t ‘Take’

I successfully installed WordPress, but when I try to make a change to the templates in Theme Editor, they will not ‘take’.

I make a change, then click ‘update’, I see a quick flash of “PHP Warning: fopen(d:\home\*******/wp-content/themes/minimaplus/header.php):failed to open stream: Permission denied in d:\home\******/wp-admin/theme-editor.php on line 58 PHP Warning: fwrite(): supplied argument is not a valid stream resource in … blah, blah blah.”
Then, it flashed back to the WordPress edit theme screen telling me my changes are successful when clearly nothing has changed.

Is this a matter of setting correct permissions at the server?

What is needed to make my admin editor work?

Thanks,

Bijou