Thanks for your help, its almost working now...
If I put the same file to the root of the site and change the links
(<?php require_once("../webassist/file_manipulation/helperphp.php"); ?> and the upload folder), its working fine...
Before that, the file was in the admin folder, the require_once link as above.
I have tried to copy the file_manipulation folder to the admin folder, changed the links, but not working.
Any idea?