IIS, Setting StatusCode (in code) will not send Response.Write message back to client

IIS 7 to IIS 8.5, if you set StatusCode (in code) other than 200, and send a response via Response.Write, the message will not be sent to the client. 

To override, and send the message set in Response.Write

 add a line like below

 Response.TrySkipIisCustomErrors = true;

this is not an issue with IIS 10+