Fel på min dator men inte på en annan!

Hej!

Vi är två som håller på med ett forum. När jag kör det han har gjort (när vi kopplar ihop allt) så får jag ett felmess som detta:

Warning: mysql_result(): Unable to jump to row 0 on MySQL result index 7 in C:\PHP_FILER\forum\forum.php on line 41

Warning: mysql_result(): Unable to jump to row 0 on MySQL result index 10 in C:\PHP_FILER\forum\forum.php on line 41

Warning: mysql_result(): Unable to jump to row 0 on MySQL result index 13 in C:\PHP_FILER\forum\forum.php on line 41

Warning: mysql_result(): Unable to jump to row 0 on MySQL result index 19 in C:\PHP_FILER\forum\forum.php on line 41

Men kommenterar jag bort den sql-satsen på rad 41 så funkar det andra. Why?
kod:

<?php
  
    include ("connect.php");
    $sql = "SELECT * FROM forum ORDER BY forum_name ASC";
  	$result = mysql_query($sql);
	
	
	
	while( $row = mysql_fetch_array($result)) {
	  echo "<tr>";
	  echo "<td><a href=\"show_forum.php?id=" . $row["id"] . "\">" . $row["forum_name"] . "</a></td>";
	  $count_topics = "SELECT COUNT(*) FROM topics WHERE forum_id=" . $row["id"];
	  $t_result = mysql_query($count_topics);
	  $t_result = mysql_result($t_result, 0);
	  echo "<td>" . $t_result . "</td>";
	  
	  $count_posts = "SELECT COUNT(*) FROM post WHERE forum_id=" . $row["id"];
  	  $p_result = mysql_query($count_posts);
  	  $p_result = mysql_result($p_result, 0);
	  echo "<td>" . $p_result . "</td>";
      
	  $latest = "SELECT post_date FROM post WHERE forum_id=" . $row["id"];
  	  $l_result = mysql_query($latest);
  	  $l_result = mysql_result($l_result, 0);
	  echo "<td>" . $l_result . "</td>";
	  echo "</tr>"; 
	 
	   } 
  ?>