The Error Message itself depicts that there is some problem in web service communication(configuration problem or connection problem).
-->By seeing your url first confirms that you are accessing service from the same machine where your service is located. as localhost is present in URL if that is not the case then please change localhost with the ip address or machine name where exactly your service is deployed. (silly suggestion but might be a problem).
-->Second thing please verify that URL is correct and there is no problem with the URL u had configured in your browser.
--> Third thing try to access the
http://localhost:999/DE.Web/WCFServices/DE_Service.svc[
^] service from where u are runnning your code by pasting above url in your browser.
if it fails then your service is not in running mode.
Please check above steps and if it still not running then there might be some connection issue between service and consumer application
Hope it helps.