HttpWebRequest automatically appends an Expect: 100-continue header for POST requests. Various sources around the internet suggest that this can be dis
HttpWebRequest
Expect: 100-continue
The HttpWebRequest class has a property called ServicePoint which can be used to change this setting for a specific request. For example:
ServicePoint
var req = (HttpWebRequest) WebRequest.Create(...); req.ServicePoint.Expect100Continue = false;