For all those that are having issues with grabbing the cookie variable for username and plugging it in your session variable, here's a simple solution that works 100%.

In your tpl page (usually header.tpl since it loads first on every page) put this at the top right after the <body> tag:
Code:
{include_php file="sc.php"}

In the sc.php page put this, and only this:
Code:
<?php
session_start();
if ($_COOKIE['vshare_user'] != "") {
  $_SESSION['USERNAME'] = $_COOKIE['vshare_user'];
}
?>
This way, you're starting your session, and technically including a cookie check. If the cookie exists, then your session username will be populated with the proper cookie username (vshare_user).

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