Dropbox recently introduced a new version of their APIs, and announced that the original API is deprecated and will stop working in around a year's time. The Objective-C framework has just arrived, and — as promised — we have added support for this in Ensembles 2. (Support in the open-source Ensembles v1.x will be added at a later date.)
Currently, you will need access to the master branch of the private repo of Ensembles to use the new class. The Idiomatic sample app has been updated to demonstrate usage of the new backend class.
The new API should be more stable, perhaps faster, and has the advantage that uploads are muted, which means your users will not see lots of notifications with gibberish file names.
Unfortunately, the authentication process is slightly different in the new version. What this means is that your app will need to deleech, and leech again. Assuming you have everything setup right, this should happen fairly automatically, only requiring users to login to Dropbox again. You might decide it is better to wait for a major version upgrade of your app before making the step to Dropbox v2.