403 errors on all pages after activating plugin

Dear all,

I’m having a problem while running this plugin. Installation and everything went smooth, but when I tick the ‘secure post’ box on one of my pages, said page and all other (parent) pages above it, up to the homepage, will display a 403, (not a 404) error. When they do this, https:// and the little lock are displayed in the URL, but the page is just not showing. I thought it’s odd that it gives me a 403 while I am logged into wordpress as an administrator.
I’ve tried it on various pages, and tried to change the permalink settings to default to detect the problem, but to no avail. I only want two pages to be secure, but if the solution is to secure the entire site, that’s also fine. Can anyone advise me?

Thanks!!

Sophie

https://wordpress.org/plugins/wordpress-https/