什么设置会导致mkdir失败？

I'm trying to set up a portal for our customers to upload a file (only we need to see it). Once they upload it, I want it to go into a particular directory.

(This snippet is a part of a code that checks file type, etc)

error_reporting(E_ALL);
date_default_timezone_set('America/New_York');
$date = date('Y_m_d_H_i_s_'.substr((string)microtime(), 2, 7));
$pathway = "uploads/" . $date;
mkdir("$pathway", 0, True);
chmod("$pathway", 0775);
move_uploaded_file($_FILES["file"]["tmp_name"], "./uploads/" . $date . "/" . $_FILES["file"]["name"]);
echo "uploads/" . $date . "/" . $_FILES["file"]["name"];

This code works fine in my development environment on my pc (Apache, PHP, MYSQL), but I can't get it to work on my hosted webservers, either the IIS server or a Linux/Apache.

So my question is, what settings do I need to change to make this work?