archive-post_type.php not working!

I tried creating a archive page template for my custom post type, archive-post_type.php as indicated on this codex page.

http://codex.wordpress.org/Post_Type_Templates

But, the the custom archive-post_type.php is not being recognized. I have Has Archive set to true. When I click on the taxonomy link, it goes to the default archive.php

Please help.

http://wordpress.org/extend/plugins/custom-post-type-ui/