"Server configuration error" is the reason ;-)
It is choosing to serve PHP files as "plain content" instead of handing them to a PHP engine for processing. This doesn't have anything to do with SSL (it will just as happily send the "plain content" over a secure connection).
From PHP: Installation:
AddModule mod_php.c
LoadModule php_module modules/mod_php.so
LoadModule php5_module modules/libphp5.so
AddType application/x-httpd-php .php
And from PHP pages won't load:
AddType application/x-httpd-php .php
AddType application/x-httpd-php-source .phps
See a pattern? :-) In any case, read the fine installation instructions for the particular platform/server.
Happy coding.
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