Fix categories and tags in wordpress custom post_type

By default word press does not look in to custom post_types for categories and tags, even though the category names are visible you get a NOT FOUND page when you click on the category.

A work around found for this issue is :

Edit : functions.php

add_filter('pre_get_posts', 'query_post_type');
function query_post_type($query) {
if(is_category() || is_tag()) {
$post_type = get_query_var('post_type');
if($post_type)
$post_type = $post_type;
else
$post_type = array('post','custom_post_type_name','nav_menu_item'); // replace custom_post_type_name with your post_type, and keep nav_menu_item to display menu in category page.
$query->set('post_type',$post_type);
return $query;
}
}

Reference: http://wordpress.org/support/topic/custom-post-type-tagscategories-archive-page

Thanks to paranoid  for guiding to the fix . ;)

./arun