Doesn't see filesystem file tree

I install modx and work, but i don't see the filesystem file.
So i create in assets/test/ with some image but i don't see the content i can upload but in mod don't see the file.
The modx log don't help me.
My modxversion is:
MODX Revolution 2.4.2-pl
My phpVersion is:
PHP Version 5.4.45
Why ? [ed. note: cristianb88 last edited this post 8 years, 1 month ago.]

I found and resolve the problem. In this file:
/public_html/core/model/modx/sources/modaccessmediasource.class.php
there is this line:
$ext = $useMultibyte ? mb_strtolower($ext, $encoding) : strtolower($ext);
i found this error on php:

and then i replace the line with:
$ext = $useMultibyte ? strtolower($ext, $encoding) : strtolower($ext);

Or, you could install multibyte string extension: http://php.net/manual/en/mbstring.installation.php