Falcon Pro, one of the most popular third-party Android Twitter clients, has hit the infamous 100,000-user token limit. This means that unless you've already used and authorized Falcon Pro, you're not going to be able to log into Twitter from the app.
That, in a word, sucks. But neither should it surprise anyone.
Before you go and start leaving one-star reviews and whining on Google Play, you need to understand what happened, and who is at fault. Last August, Twitter announced it would be updating its API. Two major changes from that update come into play here. The first is that every call back to Twitter requires authentication, and that the number of tokens used to authenticate would be capped at 100,000 for new applications. If an existing application already has more than 100,000 users, its cap is set at double its existing user base. It sounds complicated, but what it means is that if someone were to build a Twitter client (like let's say, Falcon Pro) only 100,000 users could log into Twitter using it. Twitter can grant an exception, but they haven't yet as far as anyone is aware.
That's the why, now a look at who to blame for it. It's not the application developer's fault. Twitter makes them jump through hoops, and the folks building Twitter apps like Falcon Pro do a good job working inside Twitter's strict parameters. But the 100,000 token (read: user) limit can't be worked around. Twitter puts it there so no one third-party client can become dominant, or more popular than their own lackluster app. The cause of this one all lies at Twitter's feet.
What can we do, you ask? Well the first thing you'll want to do is release any tokens you're not using. This makes them available to someone else, and every little bit helps. After that, there's not much we can do about it. There's a petition going around about Falcon Pro hitting the limit, but Twitter isn't going to change policy over a petition. You've got two choices: find a different Twitter app, or stop using the service and vote with your feet.
I'm doing the latter.