OK,

I put it into dev mode, and something else comes up now:

[Notice] Undefined variable: _SESSION
GET /silverstripe/

Line 105 in /.../sapphire/core/control/Director.php
Source

96          @file_get_contents('php://input')
97       );
98       
99       // @todo find better way to extract HTTP headers
100       if(isset($_SERVER['HTTP_ACCEPT'])) $req->addHeader("Accept", $_SERVER['HTTP_ACCEPT']);
101       if(isset($_SERVER['CONTENT_TYPE'])) $req->addHeader("Content-Type", $_SERVER['CONTENT_TYPE']);
102       if(isset($_SERVER['HTTP_REFERER'])) $req->addHeader("Referer", $_SERVER['HTTP_REFERER']);
103
104       // Load the session into the controller
105       $session = new Session($_SESSION);
106       $result = Director::handleRequest($req, $session);
107       $session->inst_save();
108
109       // Return code for a redirection request
110       if(is_string($result) && substr($result,0,9) == 'redirect:') {
111          $response = new HTTPResponse();

Trace

* Director::direct(/)
Line 115 of main.php

Any ideas?

just had the same error msg (Undefined variable: _SESSION), and found out it's because my php files were encoded in regular UTF-8. converted them to 'UTF-8 without BOM' and it works now...