twenty ten – category_id=3 not working in page for displaying post of cat3

Hy on my local server if i use the text [category_id=3] for displaying only the posts of cat 3, it works !!
i have put the same code in the home page of the running server with my site, and the same code not run , non post is displayed and the text is echoed on the page but not recongized …
thanks luca