Why does the validator complain?

Dir Sir,

Why doew the validator complain as follows?
(incl. Japanese)

URI : http://www.lilyland.net/css/main_ad.css
Line : 0 font-family: 一般フォントファミリー名(generic font family)を最後の選択肢として付け加えておく事を推奨します
検証したスタイルシートを以下に示します
body {
font-family : "?l?r ?o?S?V?b?N", "Osaka", sans-serif; 
font-size : 90%; 
color : #333300; 
margin : 0; 
padding : 0; 
background-color : #e7eef5; 
} 

I am looking forward to hearing from you as soon as possible.

Yuri N. Fukushima
Lilyland.net
webmaster@lilyland.net