New Post: null objects but valid tokens from login

Hi, we're using the Microsoft.AspNet.Identity framework to handle Twitter accounts and logins. We are successfully logging users in and getting an Access Token and Access Token Secret, but when we pass those, along with the Consumer Key/Secret (which we're successfully using during the login to get the access tokens) into your Credentials and make any requests, we're getting a NULL back.

Here are two examples:

var cred = TwitterCredentials.CreateCredentials(twitterAccessToken, twitterAccessTokenSecret, twitterConsumerKey, twitterConsumerSecret);
TwitterCredentials.ExecuteOperationWithCredentials(cred, () =>
{
    var tweet = Tweet.PublishTweet(tweetStatus);
    comment.TwitterStatusId = tweet.IdStr;
});

and

ILoggedUser loggedUser = null;
var cred = TwitterCredentials.CreateCredentials(accessToken, accessTokenSecret, twitterConsumerKey, twitterConsumerSecret));
TwitterCredentials.ExecuteOperationWithCredentials(cred, () =>
{
    loggedUser = Tweetinvi.User.GetLoggedUser();
});

In both cases, while debugging, I can see that the "cred" object has all four values correctly, but in both cases, the "tweet" and "loggedUser" objects are returned null.

I'm not sure what to troubleshoot to figure out why they're returning null. Are the credentials somehow wrong? We have our App permissions set to Read/Write.

Any help would be much appreciated!

Thanks.