private static function _getOutputErrorMsg($errno, $errmsg, $filename, $linenum, $back_trace)
    {
        // timestamp for the error entry
        date_default_timezone_set('GMT'); // to avoid error PHP 5.1
        $dt = date("Y-m-d H:i:s (T)");
        // TODO: use CSS class for style
        $err = "<div style='font-size: 12px; color: blue; font-family:Arial; font-weight:bold;'>\n";
        $err .= "[$dt] An exception occurred while executing this script:<br>\n";
        $err .= "Error message: <font color=maroon> #$errno, $errmsg</font><br>\n";
        $err .= "Script name and line number of error: <font color=maroon>$filename:$linenum</font><br>\n";
        $err .= "<div style='font-weight:normal;'>" . $back_trace . "</div>\n";
        //$err .= "Variable state when error occurred: $vars<br>";
        $err .= "<hr>";
        $err .= "Please ask system administrator for help...</div>\n";
        if ((defined('CLI') && CLI) || self::$errorMode == 'text') {
            $err = strip_tags($err);
        }
        return $err;
    }