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\v4.0.30319\aspnet_regiis.exe -ir

C:\Windows\Microsoft.NET\Framework\v3.5\Windows Communication Foundation>Service

ModelReg.exe -i

If you are using Windows 8/2012 IIS 8, then please make sure HTTP Activation for WCF is enabled as shown below.