New Post: null objects but valid tokens from login

StatusCode: 401, Details: "Could not authenticate you"

And I tried to serialize the exception object itself in case that was helpful:
{"ClassName":"Tweetinvi.Logic.Exceptions.TwitterException","Message":"Operation is not valid due to the current state of the object.","Data":null,"InnerException":null,"HelpURL":null,"StackTraceString":" at Tweetinvi.WebLogic.WebRequestExecutor.ExecuteWebRequest(HttpWebRequest httpWebRequest)\r\n at Tweetinvi.WebLogic.TwitterRequester.ExecuteQuery(String url, HttpMethod httpMethod, IEnumerable`1 headers)\r\n at Tweetinvi.Credentials.TwitterAccessor.ExecuteQuery(String query, HttpMethod method)","RemoteStackTraceString":null,"RemoteStackIndex":0,"ExceptionMethod":"8\nExecuteWebRequest\nTweetinvi.WebLogic, Version=0.9.3.3, Culture=neutral, PublicKeyToken=null\nTweetinvi.WebLogic.WebRequestExecutor\nSystem.String ExecuteWebRequest(System.Net.HttpWebRequest)","HResult":-2146233079,"Source":"Tweetinvi.WebLogic","WatsonBuckets":null}

The access token and access secret have just been returned via the login window using the same consumer key and consumer secret, so I don't understand why it would think it can't authenticate us?