atlaaaast !, something got work
sorry for being very late, but, after i got failed from the first attempt, i was discorreged. i gave it another try, .
i had to download the program first .. ie. WinMerge (a great freeware tool )
comparing with your source code, it not run on the first run, thus was giving the same previos error message, that was because :-
in your submitted file
:: Modle_diff4 > lib > weblib.php
// include($CFG->dirroot.'/'.$textfilter);
include("$CFG->dirroot/$textfilter/filter.php");