There is another small update (2.11.7) released for WhatsApp Messenger. This would solve the crash problems. The latest update (v2.11.6) which appeared last Monday and offered a solution for slowness, made the app for both iOS 4 and 5-user unusable. A bug in the app ensures that it immediately crashes when you open the app.
A growing number of users complained via the App Store on the problems and in the comments on iAppsclub itself the problem was referred to several times. According WhatsApp only users with iOS 4 or 5 affected by the bug, the app works with other iOS versions as it should. The update is now available.