Here's a better way to do it IMO...
PHP Code:
-----OPEN newreply.php-------
-----FIND------
updateuserforum($threadinfo['forumid']);
-----ADD AFTER IT------
//START NO DOUBLEPOSTS v1.0
$ddp = $DB_site->query_first("SELECT * FROM post WHERE threadid='$threadid' AND visible=1 ORDER BY postid DESC LIMIT 1");
$dpp = $ddp['userid'];
if ($bbuserinfo['userid'] == $dpp){
eval("dooutput(\"".gettemplate("nodoublepost")."\");");
}
//END NO DOUBLEPOSTS v1.0
-----SAVE&UPLOAD newreply.php--------