You don't have permission to access index.php
The site has a custom theme, but no modifications were made to any core files.
I created a test page type and test form that have the minimal Concrete5 code and the form block loads, but the submit still fails.
If check folder and page permissions and all seem correct.
In the URL string that is sent when the form is submitted &btask=passthru causes the "forbidden" error.
Any advice on the cause or how to debug this would be appreciated.