I know that this problem is in many forums and also here... but I really do not find a solution and my hoster is telling me that the problem is not a server but a script problem.
Here is the error message after clicking the button for the filemanager:
The server didn't send back a proper XML response. Please contact your system administrator. XML request error: Forbidden (403) Requested URL: http://www.domain.com/admin/includes/modules/fckeditor/editor/filemanager/connectors/php/connector.php?ServerPath=%2F&Command=GetFoldersAndFiles&Type=Image&CurrentFolder=%2F&uuid=1216384759220 Response text: <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> <HTML><HEAD> <TITLE>403 Forbidden</TITLE> </HEAD><BODY> <H1>Forbidden</H1> You don't have permission to access /admin/includes/modules/fckeditor/editor/filemanager/connectors/php/connector.php on this server.<P> <P>Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request. </BODY></HTML>