Ok, simple fix. It just wasn't validating to true - I missed an <input>
But that's the alternate fix - this one's easier. Open up private.php and find:
Code:
if ($reply=="true") {
$DB_site->query("UPDATE privatercvd SET repliedto=1 WHERE msgid=$replyto");
}
Replace with:
Code:
if ($replyto) {
$DB_site->query("UPDATE privatercvd SET repliedto=1 WHERE msgid=$replyto");
}