http://developers.de/blogs/damir_dobric/archive/2013/11/26/setting-content-type-fails-with-invfalidoperationexception.aspxWhen consuming REST Web Service like WebApi based service from Windows Phone you will sometimes have to set the content-type header to some value. This is for example the case when you want to serialize the body of the POST request like shown below:  enCommunityServer 2008 SP1 (Build: 30619.63)