Content-Length mismatch: Request Header indicated x bytes, but client sent 0 bytes.

I have been working some code to upload a file to SoundCloud with the WWW class (http://answers.unity3d.com/questions/966993/www-wwwform-and-soundcloud.html). I can't get it to work so i started the thread in the link above. Now after some more investigation it seems that the problem is that the WWW class is not sending the files i add with wwwform.AddBinaryData.

Does someone know what i am doing wrong?

 public IEnumerator UploadFileWebClient(FileInfo file)
     {
         //Started as Coroutine

         ServicePointManager.Expect100Continue = false;
         byte[] fileContents = File.ReadAllBytes(file.FullName);
 
         WWWForm form = new WWWForm();
 
         form.AddField("track[title]", "Some title");
         form.AddField("track[sharing]", "private");
         form.AddField("oauth_token", soundCloudToken);
         form.AddField("format", "json");
         form.AddBinaryData("track[asset_data]", fileContents, file.FullName, "multipart/form-data"); //Also tried "application/octet-stream"
 
         WWW download = new WWW("https://api.soundcloud.com/tracks", form);
         yield return download;
 
         if(!string.IsNullOrEmpty(download.error)) 
         {
             Debug.Log ( "Error downloading: " + download.error );
         } 
         else 
         {
             Debug.Log(download.text);
         }
     }