Problem with drop down with custom categories

Hi,

I am having an issue with using a custom category. The category is called counties and has the following entries:

Warwickshire
West Lothian
Westmorland
Wiltshire
Worcestershire
Yorkshire

I can make these counties appear and list out by doing:

<?php wp_dropdown_categories( 'taxonomy=counties' ); ?>
<input type="submit" name="submit" value="view counties" />

But whenever I select one and click the submit button it simply takes me to a 404 page.

I have tried creating a category-counties.php file but this doesn’t work either. Any help appreciated.