archive-{posttype}.php and GET query

Hi,

Sorry for this double-post (I have already posted this question in the how-to forum), but I noticed that it fits better in this forum.

I have registered a post type called “product”. With the following query I can list all the posts of this post type:

http://mysite/?post_type=product

I have also created a file archive-product.php in order to customize this display (following http://codex.wordpress.org/Template_Hierarchy#Custom_Post_Types_display), this file is however ignored! Can someone give me the reason for this and tell me what I do wrong?

Thanks in advance!