Assembly: System.Net (in System.Net.dll)
The request scheme specified in uri is not supported by this IWebRequestCreate instance.
uri is null.
The caller does not have permission to connect to the requested URI or a URI that the request is redirected to.
The URI specified in uri is not a valid URI.
The method must return an initialized instance of the WebRequest descendant that is capable of performing a standard request/response transaction for the protocol without needing any protocol-specific fields modified.