Same problem here from IOS. I reset the keys and that fixed it, for now. My first set of keys lasted all of an hour before they stopped working.
Note that when you reset the keys it takes a minute to display even if you reload.
Also, there appear to be two app management portals where you can view the status of your app
https://dev.twitter.com/
On the second site, some of the settings do not even get saved when you change them, wonderful. I don’t know if using one site or the other to manage your app contributes to token issues.