Setting the httprequestheader.date

[C# Programming]

It sounds really stupid, but I can't seem to override the Date header in a httpwebrequest. Whenever (and however) I try I keep getting the ArgumentException (This header must be modified using the appropriate property.).

Currently my code looks like this:


DateTime dt = DateTime.Now;
idmReq.Headers.Set(HttpRequestHeader.Date, dt.ToString());

I also tried these:
idmReq.Headers["Date"] = dt.ToString();
idmReq.Headers.Set("Date", dt.ToString());
idmReq.Headers.Add("Date", dt.ToString());

The problem is that I need to set the Date header for our centralized identity management system.

Can someone please help?