Strange behavior for files in /app/webroot when using ajax - ajax

Question

In my cakePHP v2.* I had a completely working application that does an ajax post to a file in /app/webroot/lib/upload/process.php
I now moved the site to a new server and get a missing controller error when I do the ajax post to the same file. So my first thought would be that somehow mod_rewrite wasn't configured... But the strangest thing is, when I access the file from my browser no error is shown. So only with the ajax call
BTW. I am running the site on an Ubuntu 14.04 server using ISPConfig as management console
The error I get is:
Missing Controller
Error: LibController could not be found.
Error: Create the class LibController below in file: app/Controller/LibController.php
And the ajax script is:
$('#my-upload-form').submit(function() {
$(this).ajaxSubmit(options);
return false;
});
Where the form is:
<form action="/lib/upload/process.php" method="post" enctype="multipart/form-data" id="my-upload-form">
Console:
Request URL:https://www.bukadoo.com/lib/upload/process.php
Request Method:POST
Status Code:404 Not Found
Remote Address:52.37.22.4:443
The .htaccess in the root:
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
RewriteRule ^$ app/webroot/ [L]
RewriteRule (.*) app/webroot/$1 [L]
</IfModule>
The .htaccess in webroot folder:
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php [QSA,L]
</IfModule>

Answer 1

Well in the end it was a server issue. After installing the application on a whole different server things were working fine.
After a long search I found out that I needed to set the settings in ISPConfig from Fast-CGI to Mod-PHP