You can get the message "This collection already contains an address with scheme http. There can be at most one address per scheme in this collection." when using REST. If so, please read this article: kb.discountasp.net/KB/a799/error-accessing-wcf-service-this-collection-already.aspx. You can add the mentioned configuration section between </system.webServer> and </configuration> in your web.config. 
 

-hg-