ProStar Logistics have made a change to the URL of their rating API over the weekend of 25th April 2015. You will no longer receive accurate rates via ProStar if you have not updated your Magento site.
WebShopApps have released an updated version of our Freight extension to include the updated URL for ProStar. You should still see rates using the old URL but you should update to the latest version at your earliest convenience to guarantee that your rates are correct.
You can contact sales@webshopapps.com for the latest version or download from your WebShopApps downloads.