Hi MikeJuri,
Got this issue because the uploader gets the wrong path of the resource files. Please try the way below, it will fix this issue.
1. open file \phpuploader\include_phpuploader.php
2. find section below
$cd=dirname($this->GetWebPath(__FILE__));
3. change it to
$cd=dirname($_SERVER['SCRIPT_NAME']).'/phpuploader';
Regards,
Ken