I know PHP is working, because when I browse directly to a file in wwwroot, it's served fine. And the virtual directory is working, because when I browse to html files in the virtual directory, they're served. But when I browse to a PHP file in the virtual directory, I receive an HTTP 500 error from IIS.
Searching on the web, I found a bunch of suggestions to confirm that doc_root in php.ini is blank - however, it is and it's still not working.
Other configuration settings going on: Integrated Windows authentication is turned on, client certificates are required, and client certificate mapping is enabled. All of it is working fine for PHP content not in a virtual directory.
Thanks for any suggestions!