The problem is that wp_nav_menu() should really only ever be calling theme_location, not menu.
The Theme defines menu locations, and then places those menu locations in the template. The user defines menus, and assigns menus to theme locations.
So, change this:
<?php wp_nav_menu('menu=services_menu'); ?>
…to this:
<?php wp_nav_menu( 'theme_location=services_menu' ); ?>