Error when using the Upload API: "The remote server returned an error: (401) Unauthorized."

JakeC

I am trying to use the https://upload.smugmug.com/ API to upload an image to a gallery, but I'm getting a "The remote server returned an error: (401) Unauthorized." error message when sending the POST request. I have an access token and I'm building the authorization header like so:

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://upload.smugmug.com/");
authString = "oauth_consumer_key=[CONSUMER_KEY], oauth_nonce=" + GetNonce() + ", oauth_signature='[CONSUMER_SECRET]', oauth_signature_method='HMAC-SHA1', oauth_timestamp=" + GetTimeStamp() + ", oauth_token='[ACCESS_TOKEN]', oauth_token_secret='[ACCESS_TOKEN_SECRET]', oauth_version='1.0'"; request.Headers.Add("Authorization", authHeader);

I'm also building the rest of the headers like so:

request.Headers.Add("X-Smug-AlbumUri", "/api/v2/album/ABLUMKEY");
request.Headers.Add("X-Smug-AlbumID", "ALBUMID");
request.Headers.Add("X-Smug-ResponseType", "JSON");
request.Headers.Add("X-Smug-Version", "v2");
request.Headers.Add("X-Smug-Caption", tbCaption.Text); //Caption
request.Headers.Add("X-Smug-FileName", Request.Files[0].FileName);

request.ContentType = "application/x-www-form-urlencoded";
request.Method = "POST";
request.Headers.Add("Authorization", authHeader);
request.Accept = "application/json";

try
{
//Get Request Stream
var image = System.Drawing.Image.FromStream(Request.Files[0].InputStream);
var dataStream = ConvertImageToByteArray(image);

Stream newStream = request.GetRequestStream();
newStream.Write(dataStream, 0, dataStream.Length);
newStream.Close();
//END - Get Request Stream


var httpResponse = (HttpWebResponse)request.GetResponse();

string output = string.Empty;

using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
{
var result = streamReader.ReadToEnd();
}
}

JakeC

Also, The purpose of my project is be able to upload images from my desktop via the API to an existing album. Does it look like I'm missing anything?