Re: Sorry, that file cannot be edited
@StevieG adding footer.php from bp-default to your child theme shouldn’t mess with your install.
So going back to “If I try to access the files in my child theme I get the error message ‘Sorry, that file cannot be edited’.” is this in relation to editing the child theme files via Network Admin > Appearance > Editor panel? If not, what files are you trying to edit and where?
EDIT- just found out you posted same topic in WP Forums and the problem as posted there was clearer 
