I wanted to access an internal REST API from Silverlight, but it turns out that I am not allowed to use POST or DELETE as the HTTP method for my request.
Doing so always
Another solution I came up with is setting in RestSharp the X-HTTP-Method-Override header, and just send POST request.
This might also be useful if you can just modify the client code, but the server has an unusuable clientaccesspolicy.xml.
In my API class I use this code
if (request.Method == Method.PUT || request.Method == Method.DELETE)
{
request.AddHeader("X-HTTP-Method-Override", request.Method.ToString());
request.Method = Method.POST;
}