Recently twitter implemented some limitations on third-party developers that meant that some applications were restricted in the amount of users that can register for the application.
This meant that some popular applications found problems, one of the most recent of whom is the popular application Tweetbot, which has today been removed from the Mac App Store due to these restrictions.
Since the removal a number of users have seen a number of error messages, stating that the application cannot authenticate more users at this time.
This was later confirmed via a Tweet from Tweetbot:
We are aware of Tweetbot for Mac authentication issues. We have contacted Twitter and are waiting for a response. Thanks for your patience.
— Tweetbot by Tapbots (@tweetbot) January 25, 2015
What this means is that Twitter’s limit on API tokens for third parties has come into effect, which was the same problem for the Twitterrific application, which was also removed because of the same errors.
You can find out more about the issues at the 9to5mac link below.