How did you create the child theme - see:
http://codex.wordpress.org/Child_Themes
Child themes should not contain a copy of the parent theme style.css file.
It's also possible that your theme will not work with a child theme - you'll need to ask the developer about that - as we have no way to support commercial themes here, sorry.
If you post a link to your site, someone might be able to see if something is obviously wrong, though.