mysql_error problem

I am using the below function (error_db) witch is called thus:- function query_db( $sql, $db ) {

    $result = mysql_query( $sql, $db ) or
      error_db( $sql, $db );
    return $result;

} But $sqlerr is always blank (it is set with '$sqlerr = mysql_error( $db );'). Any idea why? Ben function error_db( $sql, $db ) {

    global $SERVER_NAME;
    global $SCRIPT_NAME;

    table_top( "Database Error" );

    table_middle();

    $sqlerr = mysql_error( $db );

    echo "<b>SQL:</b>:<BR>$sql<br><b>Error:</b><BR>$sqlerr";

    table_bottom();

    // Clost of table/html from calling script
    table_bottom();
    html_footer();

    // Send error via email

    $msg  =
      "Database error has accured on $SERVER_NAME\n\n.".
      "The error message is :-\n\n".
      "SQL:$sql\n\nError:$sqlerr\n\n".
      "This message was ".
      "generated by '$SERVER_NAME$SCRIPT_NAME'";

    $subj = "Database error from $SERVER_NAME";

    // Hard coded to minimize chance of this module erroring
    $to   = "ben@videonetwork.org";
    $from = "From: ".$to;

    mail( $to, $subj, $msg, $from );

    die();

} ****************************************************************

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