I get this error in the acp when they try to:
XenForo_Exception: Cannot insert a message in the middle of a discussion. - library\XenForo\DataWriter\DiscussionMessage.php:449
I've already done that stuff, I did change my time from pm to am as it was wrong on my server and people on my forums were complaining about the time being off.
Any posts with the old time that is now showing later than the actual time will not be able to be posted to until the current time is past the post time.