Mostly likely you have entered relative paths for your links (for example; widgets.html) rather than absolute paths (for example; http://www.widgetdesigns.com/widgets.html). Your custom checkout pages are served from a separate set of servers than your store pages. You will notice when clicking an order button that the URL in the address bar changes from store.widgetdesigns.com or www.widgetdesigns.com to order.store.yahoo.net (order.store.yahoo.com for the previous version of checkout). In order to correct this, please ensure than any links in your checkout regions use absolute paths to the location to which you wish to link.