It's telling you that on or near line 6 of the index.php file you are attempting to include a file via HTTP, but that the server is returning a Not Found error. Normally you do not include files via a URL, but instead via a local file system path on the server (though there are certain special occasions where you might use a URL). But it would help to see the first 10 lines of the index.php file to get some idea about what's going on (and please use the
[url=http://phpbuilder.com/board/misc.php?do=bbcode]bbCode tags[/url] around it).