If you see an error as shown, "Back-end server error. Response Code: 404, Message: Not Found"
This error can happen for couple of reasons, either IIS is not installed correctly or script maps are overwritten. Please execute the following commands and reset IIS.
C:\Windows\Microsoft.NET\Framework\v3.5\Windows Communication Foundation>Service
If you are using Windows 8/2012 IIS 8, then please make sure HTTP Activation for WCF is enabled as shown below.