Self hosted Wep Api on my Respbarry Pi leads to HTTP 400 Bad Request - asp.net-web-api

Question

I've created a self hosted Web API (Web API 2.2 + Owin). The service is quite simple and only returns the list of GPIO pin values.
On my Pi itself, it works perfectly. I can call the service without problems. Only when I try to call it from my PC a HTTP 400 is returned:
Request:
GET http://192.168.178.105/RobotApi/GetGpioPinValues HTTP/1.1
Host: 192.168.178.105
Connection: keep-alive
Accept: application/json, text/plain, */*
Origin: http://localhost
User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.95 Safari/537.36
Referer: http://localhost/piRobot.WebSite/index.html
Accept-Encoding: gzip, deflate, sdch
Accept-Language: en-US,en;q=0.8,de-DE;q=0.6,de;q=0.4
Response:
HTTP/1.1 400 Bad Request
Content-Type: text/html; charset=utf-8
Server: Mono-HTTPAPI/1.0
Date: Fri, 02 Jan 2015 16:19:24 GMT
Content-Length: 35
Connection: close
<h1>Bad Request (Invalid host)</h1>
I hope someone out there can help me. Any suggestions?
Thanks a lot,
Dante

Answer 1

Ok. Got it:-)
It was no problem with raspberry or mono or Web Api itself. The self hosted service was initialized with the base URL http://localhost. The strange thing is, the service is only available via localhost, but not via the according IP address!!!
So what I've done now is, I substituted localhost with the IP address of my Pi and it works perfectly. Now the service is only accessible via the IP?!
I still have no clue why it makes a difference, but obviously it does.