Problem selecting images

I have installed fckeditor in a website, and it works, but I have a problem. When I try to add an image (from the server) a pop-up is opening telling me: The server didn't sent back a proper XML response.
Another problem is when I try to up-load a file: nothing is happening.
That is the way I've integrated FCKeditor:

<?include("fckeditor/fckeditor.php");?>