「If the model does contain blocks or use features that postdate the earlier version, the model might not give correct results when run by the earlier version.」
下記ページの「Saving a Model in Earlier Formats」というところを見てください
http://www.mathworks.com/access/helpdesk/help/toolbox/simulink/index.html?/access/helpdesk/help/toolbox/simulink/ug/f2-82897.html&http://www.google.co.jp/search?sourceid=navclient&ie=UTF-8&rlz=1T4GGLJ_enUS254US254&q=simulink+version