Some things to look at:
($err !== false ? '<div class="error">'.$err.'</div>' : null);
This is likely why it's broken. You need to use an IF statement. The ? : format requires PHP 5.4, which is not available on Stevie (which has 5.3.8). You will need to go through your code and rewrite these as IF statements. The conditional should also be != not !==. I personally would use !empty($err) instead.
if(empty($uname) || empty($pass) || empty($uname) && empty($pass)) $err .= $t['er_login'];
No need for the "empty($uname) && empty($pass)" part in these IF statements. As soon as one of them is empty, it's true, and the other one doesn't matter.
md5(input($_POST['pass']));
Use SHA1. You also should salt your passwords.