准备发送加密信息的声明问题

This is my current statement. Everything was working fine until I added the key

Key is just a generated hash for the user to activate the account.

$stmt = $mysqli->prepare("INSERT INTO Account (accountUsername,accountPassword,accountEmail,accountActivate,accountKey) VALUES (?, ?, ?,?,?)");
$stmt->bind_param('sssiss', $username, $newPassword, $email,0,$key,time());

When I'm doing this code I'm getting an error.

Cannot pass parameter 5 by reference

Do you know what could be the issue?

Thanks!

Edit Code:

$stmt = $mysqli->prepare("INSERT INTO Account (accountUsername,accountPassword,accountEmail,accountActivate,accountKey,accountCreated) VALUES (?, ?, ?,?,?,?)");
$stmt->bind_param('sssisi', $username, $newPassword, $email,0,$key,$time);

http://i.stack.imgur.com/Th5tl.png

If you use bind_param that 0 needs to be in a variable since bind_param passes by reference.

$somevar=0;
$stmt = $mysqli->prepare("INSERT INTO Account (accountUsername,accountPassword,accountEmail,accountActivate,accountKey) VALUES (?, ?, ?, ?,?,?)");
$stmt->bind_param('sssiss', $username, $newPassword, $email,$somevar,$key,$time);