This particular error is indicating that some file in your site’s directory structure does not have permissions to be viewed by your web site. You need to ensure all files for your site are readable/executable
One easy way to debug this is to run the command line tool calcs on a different (working) web site you are hosting, then apply those permissions to your site. This can be dangerous though as it is a “blanket fix”.
If you can identify the file that has the wrong permissions you can modify them with calcs.
File that works
NT AUTHORITY\Authenticated Users:C
File causing errors
To fix the file with the incorrect permissions
cacls shop-logo.png /G "NT AUTHORITY\Authenticated Users":C /E
cacls shop-logo.png /G BUILTIN\Users:R /E