Sorry, this was discussed at punres.org. I only posted here as I could not post it there (message too long).

There were a number of missing {$db->prefix} tags. I can't reacll exactly which ones they were, but this is the corrected file.

Nullig

Here's my modchatxmlrpc.php - remember to change the forum id for your site:

<?php
define('PUN_ROOT', './');
require_once(PUN_ROOT.'include/common.php');
require_once(PUN_ROOT.'lang/'.$pun_user['language'].'/modchat.php');

/*****************************
 *   EDIT THE VALUE BELOW!   *
 *****************************
 * Chat Log Forum
 * Edit to match the ID of the forum you created where messages will be logged
 */
$db_logForum_id = 1;

/****************************************
 * DO NOT EDIT ANYTHING BELOW THIS LINE *
 ****************************************/
if($db_logForum_id == 0)
    die($lang_modchat['not configured'] . "<br />\n");
    
/* Headers
 * to match those of PunBB
 */
header('Expires: Thu, 21 Jul 1977 07:30:00 GMT');
header('Last-Modified: '.gmdate('D, d M Y H:i:s').' GMT');
header('Cache-Control: post-check=0, pre-check=0', false);
header('Pragma: no-cache');        // For HTTP/1.0 compability
header('Content-type: text/html; charset='.$lang_common['lang_encoding']);

switch($_POST['action']) {
    case 'send':
        auth();
        echo send($_POST['message']);
        break;
    case 'receive':
        auth();
        echo receive($_POST['returnall']);
        break;
    case 'toggleChat':
        echo toggleChat();
        break;
    case 'activeUsers':
        auth();    
        echo activeUsers();
        break;
    default:
        echo null;
}

function auth() {
    global $pun_user;

    if($pun_user['is_guest']) {
        exit;
    }
}

function safelyReadFile($file) {
    if(function_exists('file_get_contents')) {
        return file_get_contents($file);
    } else {
        $h = fopen($file, 'r');
        $c = fread($h, filesize($file));
        fclose($h);
        return $c;
    }
}

function toggleChat() {
    global $db, $pun_user, $lang_modchat;
    
    if(!$pun_user['is_guest']) {
        $res = $db->query("SELECT showchat 
                   FROM {$db->prefix}users 
                         WHERE id = {$pun_user['id']}");
        $format = "UPDATE {$db->prefix}users 
               SET showchat = %d 
               WHERE id = {$pun_user['id']}";
        
        if ((int)$db->result($res) === 1) {
            $qry = $db->query(sprintf($format, 0));
            return null;
        } else {
            $db->query(sprintf($format, 1));
            return safelyReadFile(PUN_ROOT.'/include/user/modchat.htm');
        }
    // user is guest
    } else {
        return "<script>alert('{$lang_modchat['guest message']}');</script>";
    }
}
                
                


function send($message = null) {    
    global $db_logForum_id, $db, $pun_user;
    $username = $db->escape($pun_user['username']);
    
    if (!is_null($message)) {    
        $topic_id = activeChat();
        $time = time();

        if (!$topic_id) {    
            $subject = date('D, M jS o g:i a');
            $res = $db->query("INSERT INTO {$db->prefix}topics (poster, subject, posted, last_post, last_poster, forum_id)
                       VALUES ('$username', '$subject', $time, $time, '$username', $db_logForum_id)") 
                       or die("SQL Error #01 <br />\n");
            $norplyinc = true;
            $topic_id = $db->insert_id();
        }
        
        $res = $db->query("INSERT INTO {$db->prefix}posts (poster, poster_id, poster_ip, message, hide_smilies, posted, topic_id)
                   VALUES ('$username', {$pun_user['id']}, '{$_SERVER['REMOTE_ADDR']}', '".$db->escape(pun_trim(utf8_tohtml($message)))."', 0, $time, $topic_id)")
                   or die("SQL Error #02 <br />\n");
        $post_id = $db->insert_id();
        
        // update forums stats
        $rplyinc = ($norplyinc) ? 0 : 1;
        updateTopic($topic_id, $post_id, $rplyinc, $username);
        update_forum($db_logForum_id);
    }

    return stripslashes(messageOutput($username, $message, $time, 'self'));
}

function updateTopic($topic_id, $post_id, $replyIncriment, $username) {
    global $db;
    
    $time = time();
    $db->query("UPDATE {$db->prefix}topics
                SET last_poster = '$username', last_post = $time, last_post_id = $post_id, num_replies = num_replies + $replyIncriment
            WHERE id = $topic_id");
}

function activeChat() {
    global $db_logForum_id, $db;
    
    $time = (time()-(60*10));
    $res = $db->query("SELECT id FROM {$db->prefix}topics
               WHERE forum_id = $db_logForum_id
               AND last_post > $time
               LIMIT 0,1");
                                         
    $topic_id = $db->result($res);
    return ($topic_id) ? $topic_id : false;
}

function messageOutput($username, $message, $time, $self = null) {
    require_once(PUN_ROOT.'/include/parser.php');
    
    $time = userTime((int)$time);
    $message = str_replace(array('<p>', '</p>'), '', parse_message($message, '0'));

    return "<span class=\"modchattimestamp\">$time</span>" .
           "<span class=\"modchatinput{$self}username\"><$username></span> " .
                 "<span class=\"modchatinput{$self}message\">". utf8_tohtml($message) ."</span><br />\n";
}

function userTime($time = false) {
    global $db, $pun_user, $pun_config;
    
    $time = ($time) ? $time : time();
    $diff = ($pun_user['timezone'] - $pun_config['o_server_timezone']) * 3600;
    $time += $diff;

    return date('g:i', $time);
}

function receive($returnall) {
    global $db, $pun_user;
    
    $return = null;
    $chat_id = activeChat();
    $username = $db->escape($pun_user['username']);

    if ($chat_id) {
        if ($returnall == 'true') {
            $res = $db->query("SELECT id,poster,message,posted
                       FROM {$db->prefix}posts
                       WHERE topic_id = $chat_id
                       ORDER BY id ASC");
        } else {
            $res = $db->query("SELECT {$db->prefix}posts.id,{$db->prefix}posts.poster,{$db->prefix}posts.message,{$db->prefix}posts.posted
                       FROM {$db->prefix}posts,{$db->prefix}users
                        WHERE {$db->prefix}posts.topic_id = $chat_id
                       AND {$db->prefix}posts.poster != '$username'
                       AND {$db->prefix}posts.id > {$pun_user['modchatlastmsg']}
                       ORDER BY {$db->prefix}posts.id ASC");
        }

        if ($db->num_rows($res) > 0) {
            while ($row = $db->fetch_assoc($res)) {
                if($lstMsg != $row['message']) {
                    $self = ($row['poster']==$pun_user['username']) ? 'self' : null;
                    $return .= messageOutput($row['poster'], $row['message'], $row['posted'], $self);
                    $id = $row['id'];
                    $lstMsg = $row['message'];
                }
            }
            
            if($id) updateUserLastMessage($id);
        }
    }
    
    return $return;
}

function updateUserLastMessage($lastMsg_id) {
    global $db, $pun_user;
    
    $db->query("UPDATE {$db->prefix}users SET modchatlastmsg = $lastMsg_id WHERE id = {$pun_user['id']}");
}

function activeUsers() {
    global $db, $lang_modchat;
    
    $ret = null;
    $res = $db->query("SELECT {$db->prefix}users.username
               FROM {$db->prefix}users,{$db->prefix}online
               WHERE {$db->prefix}users.showchat = 1
               AND {$db->prefix}online.ident = {$db->prefix}users.username
               ORDER by {$db->prefix}users.username ASC");

    while ($row = $db->fetch_assoc($res)) {
        $ret .= '<li class="modchatuser">' .$row['username'] . "</li>\n";
    }
    
    $count = count(explode("\n", $ret)) - 1;
    $unit = ($count < 2) ? $lang_modchat['user'] : $lang_modchat['users'];
    return "<span id=\"modchatTotalUsers\">$count $unit {$lang_modchat['chatting']}</span>" .
           "<br />\n<ul>\n$ret</ul>";
}

/* UTF8 helper function
 *
 * @license    LGPL (http://www.gnu.org/copyleft/lesser.html)
 * @author     Andreas Gohr <andi@splitbrain.org>
 */
function utf8_tohtml ($str) {
  $ret = '';
  $max = strlen($str);
  $last = 0;  // keeps the index of the last regular character
  for ($i=0; $i<$max; $i++) {
    $c = $str{$i};
    $c1 = ord($c);
    if ($c1>>5 == 6) {  // 110x xxxx, 110 prefix for 2 bytes unicode
      $ret .= substr($str, $last, $i-$last); // append all the regular characters we've passed
      $c1 &= 31; // remove the 3 bit two bytes prefix
      $c2 = ord($str{++$i}); // the next byte
      $c2 &= 63;  // remove the 2 bit trailing byte prefix
      $c2 |= (($c1 & 3) << 6); // last 2 bits of c1 become first 2 of c2
      $c1 >>= 2; // c1 shifts 2 to the right
      $ret .= '&#' . ($c1 * 100 + $c2) . ';'; // this is the fastest string concatenation
      $last = $i+1;
    }
  }
  return $ret . substr($str, $last, $i); // append the last batch of regular characters
}

Nullig

@ango

A couple of changes to the arcade_play.php file to make it work correctly in FF (IE seems to work OK), as the h2 tags don't work outside of the tables. Also, the $lang_arcade['Not played'] should be $lang_arcade['Not played yet'] to match the lang file.

Change:

// We have no highscore
?>
    <div class="blockform">
    <h2>
    <table cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
    <td width="33%" cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
        <span><? echo $lang_arcade['Not played'] ?></span>
    </td>
    <td width="33%" align="middle" cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
        <span align="right"><? echo $lang_arcade['Top highscore'] ?> <strong> <? echo $result2['rank_score'] ?> </strong> <? if($result2['rank_score'] > 0) echo $lang_arcade['by'], ' '?> <i> <? echo $result2['username']?></i></span>
    </td>    
    <td width="33%" align="right" cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
        <span align="right"><? echo $lang_arcade['played']?> <strong> <? echo $line['game_played'] ?><strong></span>
    </td>
    </table>
    </h2>
    
<?php
}
else
{
    $line2 = $db->fetch_assoc($result);
    
// We have a highscore
?>

<div class="blockform">
    <h2>
    <table cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
    <td width="33%" cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
        <span><? echo $lang_arcade['Your highscore'],': ' ?> <strong><? echo $line2['rank_score'] ?></strong></span>
    </td>
    <td width="33%" align="middle" cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
        <span align="right"><? echo $lang_arcade['Top highscore'] ?> <strong> <? echo $result2['rank_score'] ?> </strong> <? echo $lang_arcade['by'], ' '?> <i> <? echo $result2['username']?></i></span>
    </td>    
    <td width="33%" align="right" cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
        <span align="right"><? echo $lang_arcade['played']?> <strong> <? echo $line['game_played'] ?><strong></span>
    </td>
    </table>
    </h2>

to:

// We have no highscore
?>
    <div class="blockform">
    <table cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
    <td width="33%" cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
        <h2><span><? echo $lang_arcade['Not played yet'] ?></span></h2>
    </td>
    <td width="33%" align="middle" cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
        <h2><span align="right"><? echo $lang_arcade['Top highscore'] ?> <strong> <? echo $result2['rank_score'] ?> </strong> <? if($result2['rank_score'] > 0) echo $lang_arcade['by'], ' '?> <i> <? echo $result2['username']?></i></span></h2>
    </td>    
    <td width="33%" align="right" cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
        <h2><span align="right"><? echo $lang_arcade['played']?> <strong> <? echo $line['game_played'] ?><strong></span></h2>
    </td>
    </table>
    
<?php
}
else
{
    $line2 = $db->fetch_assoc($result);
    
// We have a highscore
?>

<div class="blockform">
    <table cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
    <td width="33%" cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
        <h2><span><? echo $lang_arcade['Your highscore'],': ' ?> <strong><? echo $line2['rank_score'] ?></strong></span></h2>
    </td>
    <td width="33%" align="middle" cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
        <h2><span align="right"><? echo $lang_arcade['Top highscore'] ?> <strong> <? echo $result2['rank_score'] ?> </strong> <? echo $lang_arcade['by'], ' '?> <i> <? echo $result2['username']?></i></span></h2>
    </td>    
    <td width="33%" align="right" cellspacing="0" style="padding: 0px 0px 0px 0px; margin-top: 0px; margin-left: 0px; margin-right: 0px; margin-bottom: 0px; border:none; ">
        <h2><span align="right"><? echo $lang_arcade['played']?> <strong> <? echo $line['game_played'] ?><strong></span></h2>
    </td>
    </table>

Nullig

I had the same problem and I found that this solved it:

Edit profile.php and look for

$datestamp = mktime(0,0,0,$month,$day,0)

change it to

$datestamp = mktime(0,0,0,$month,$day,0);

note the missing ; at the end of the line.