This is a weird one. The setup...
FMS 13 on Windows 2008 Server
DB with External storage container
PHP file to host
I needed to setup a PHP file and put it in the normal Inetpub location but it didn't work.
I got an error saying that it couldn't be found at the path: ProgramFiles>FileMaker>FileMaker server>HTTPServer>Conf
In IIS there are 2 sites shown. Default Web Site and FMWebSite. So in IIS I turned off the FMWebSite and turned on the Default Web site. PHP page worked! However, the container field would not display the images due to an error. ( I don't have the exact error but can retrieve it after hours)
So I turned the FMWebSite back on and the container field worked again. I also move the PHP file to the FileMaker path and it works locally. From the outside I get an internal server error. Web Direct works so i know the ports are mapped properly.