Warning: mysql_num_rows(): supplied

Ik krijg deze error:

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /home/war/domains/supermails.nl/public_html/admin/verbannen.php on line 59

Bij deze code:

[COLOR= #0000BB]<?php[/COLOR]
[URL="http://www.php.net/if"]if[/URL][COLOR= #007700]([/COLOR][COLOR= #0000BB]$_SERVER[/COLOR][COLOR= #007700][[/COLOR][COLOR= #DD0000]REQUEST_METHOD[/COLOR][COLOR= #007700]] ==[/COLOR] [COLOR= #DD0000]"POST"[/COLOR][COLOR= #007700])
{[/COLOR]
    [URL="http://www.php.net/if"]if[/URL][COLOR= #007700]([/COLOR][COLOR= #0000BB]$_POST[/COLOR][COLOR= #007700][[/COLOR][COLOR= #DD0000]user[/COLOR][COLOR= #007700]] ==[/COLOR] [COLOR= #DD0000]""[/COLOR][COLOR= #007700])
    {[/COLOR]
        [URL="http://www.php.net/echo"]echo[/URL][COLOR= #DD0000]"Geen naam ingevuld!"[/COLOR][COLOR= #007700];
    }[/COLOR]
    [URL="http://www.php.net/elseif"]elseif[/URL][COLOR= #007700]([/COLOR][COLOR= #0000BB]$_POST[/COLOR][COLOR= #007700][[/COLOR][COLOR= #DD0000]reden[/COLOR][COLOR= #007700]] ==[/COLOR] [COLOR= #DD0000]""[/COLOR][COLOR= #007700])
    {[/COLOR]
        [URL="http://www.php.net/echo"]echo[/URL][COLOR= #DD0000]"Je moet een reden op schrijven."[/COLOR][COLOR= #007700];
    }[/COLOR]
    [URL="http://www.php.net/elseif"]elseif[/URL][COLOR= #007700]([/COLOR][COLOR= #0000BB]$_POST[/COLOR][COLOR= #007700][[/COLOR][COLOR= #DD0000]datum[/COLOR][COLOR= #007700]] ==[/COLOR] [COLOR= #DD0000]""[/COLOR][COLOR= #007700])
    {[/COLOR]
        [URL="http://www.php.net/echo"]echo[/URL][COLOR= #DD0000]"Je moet een datum ingeven."[/COLOR][COLOR= #007700];
    }[/COLOR]
    [URL="http://www.php.net/else"]else[/URL]
    [COLOR= #007700]{[/COLOR]
      [COLOR= #0000BB]$result[/COLOR] [COLOR= #007700]=[/COLOR] [URL="http://www.php.net/mysql_query"]mysql_query[/URL][COLOR= #007700]([/COLOR][COLOR= #DD0000]"select * from users where username=$_POST[user]"[/COLOR][COLOR= #007700])[/COLOR] or [URL="http://www.php.net/die"]die[/URL][COLOR= #007700]([/COLOR][URL="http://www.php.net/mysql_error"]mysql_error[/URL][COLOR= #007700]());[/COLOR]
      
        [COLOR= #0000BB]$sel[/COLOR] [COLOR= #007700]=[/COLOR] [URL="http://www.php.net/mysql_query"]mysql_query[/URL][COLOR= #007700]([/COLOR][COLOR= #DD0000]"SELECT username FROM verbannen WHERE username = "[/COLOR][COLOR= #007700].[/COLOR][COLOR= #0000BB]$_POST[/COLOR][COLOR= #007700][[/COLOR][COLOR= #DD0000]user[/COLOR][COLOR= #007700]]);[/COLOR]
        
        [URL="http://www.php.net/if"]if[/URL][COLOR= #007700]([/COLOR][URL="http://www.php.net/mysql_num_rows"]mysql_num_rows[/URL][COLOR= #007700]([/COLOR][COLOR= #0000BB]$sel[/COLOR][COLOR= #007700]) ==[/COLOR] [COLOR= #0000BB]1[/COLOR][COLOR= #007700])[/COLOR] [COLOR= #FF8000]//staat al in de database, dus verwijderen[/COLOR]
        [COLOR= #007700]{[/COLOR]
        
          [URL="http://www.php.net/mysql_query"]mysql_query[/URL][COLOR= #007700]([/COLOR][COLOR= #DD0000]"DELETE FROM verbannen WHERE username = "[/COLOR][COLOR= #007700].[/COLOR][COLOR= #0000BB]$_POST[/COLOR][COLOR= #007700][[/COLOR][COLOR= #DD0000]user[/COLOR][COLOR= #007700]]);
          
        }[/COLOR]
          [COLOR= #FF8000]//nu verdergaan met in de database zetten[/COLOR]
          [URL="http://www.php.net/if"]if[/URL][COLOR= #007700]([/COLOR][COLOR= #0000BB]$row[/COLOR] [COLOR= #007700]=[/COLOR] [URL="http://www.php.net/mysql_fetch_Array"]mysql_fetch_Array[/URL][COLOR= #007700]([/COLOR][COLOR= #0000BB]$result[/COLOR][COLOR= #007700]))
          {[/COLOR]
              [URL="http://www.php.net/mysql_query"]mysql_query[/URL][COLOR= #007700]([/COLOR][COLOR= #DD0000]"INSERT INTO verbannen (username, reden, datum, sinds) VALUES ("[/COLOR][COLOR= #007700].[/COLOR][COLOR= #0000BB]$_POST[/COLOR][COLOR= #007700][[/COLOR][COLOR= #DD0000]user[/COLOR][COLOR= #007700]].[/COLOR][COLOR= #DD0000]", "[/COLOR][COLOR= #007700].[/COLOR][COLOR= #0000BB]$_POST[/COLOR][COLOR= #007700][[/COLOR][COLOR= #DD0000]reden[/COLOR][COLOR= #007700]].[/COLOR][COLOR= #DD0000]", "[/COLOR][COLOR= #007700].[/COLOR][COLOR= #0000BB]$_POST[/COLOR][COLOR= #007700][[/COLOR][COLOR= #DD0000]datum[/COLOR][COLOR= #007700]].[/COLOR][COLOR= #DD0000]", "[/COLOR][COLOR= #007700].[/COLOR][URL="http://www.php.net/date"]date[/URL][COLOR= #007700]([/COLOR][COLOR= #DD0000]"d/m/Y H:i:s"[/COLOR][COLOR= #007700]).[/COLOR][COLOR= #DD0000]")"[/COLOR][COLOR= #007700])[/COLOR] or [URL="http://www.php.net/print"]print[/URL][COLOR= #007700]([/COLOR][URL="http://www.php.net/mysql_error"]mysql_error[/URL][COLOR= #007700]());[/COLOR]
              [URL="http://www.php.net/echo"]echo[/URL] [COLOR= #DD0000]De user [/COLOR] [COLOR= #007700].[/COLOR] [COLOR= #0000BB]$_POST[/COLOR][COLOR= #007700][[/COLOR][COLOR= #DD0000]user[/COLOR][COLOR= #007700]] .[/COLOR] [COLOR= #DD0000] is verbannen tot [/COLOR] [COLOR= #007700].[/COLOR] [COLOR= #0000BB]$_POST[/COLOR][COLOR= #007700][[/COLOR][COLOR= #DD0000]datum[/COLOR][COLOR= #007700]] .[/COLOR][COLOR= #DD0000][/COLOR][COLOR= #007700];
          }[/COLOR]
          [URL="http://www.php.net/else"]else[/URL]
          [COLOR= #007700]{[/COLOR]
              [URL="http://www.php.net/echo"]echo[/URL] [COLOR= #DD0000]De naam die je hebt ingevoert staat niet in ons bestand[/COLOR][COLOR= #007700];
          }
            
    }
}[/COLOR]
[URL="http://www.php.net/else"]else[/URL]
[COLOR= #007700]{[/COLOR]
?>  
</p>
    <form name="form1" method="post" action="">
  <font size="2" face="Verdana, Arial, Helvetica, sans-serif"> Gebruikersnaam:<br>
  <input name="user" type="text" id="user">
  <br>
  Reden:<br />
  <textarea name="reden" cols="40" rows="10"></textarea><br />
  <br />
  *Datum:<br />
  <input name="datum" type="datum" id="datum" value="00/00/0000">
  <br />
  <input type="submit" name="Submit" value="Verzenden">
  </font>
  <br />* = De datum moet altijd 00/00/0000 zijn.
</form>
[COLOR= #0000BB]<?[/COLOR]
[COLOR= #007700]}[/COLOR]
?>

Waar aan kan dat liggen?

let eens op je querys man

verander

SELECT username FROM verbannen WHERE username = ".$_POST[user]

door

SELECT username FROM verbannen WHERE username = ".$_POST[user]."

Oeps, mijn fout jongens Het is nog vroeg