Q: Kakuro won't open anymore.
A: Since version 2.11 and the introduction of iOS4, there have been instances where Kakuro will no longer work. To fix this issue please do the following:
1. Remove the app from your device by pressing and holding down on the Kakuro icon until an "x" appears on the icon. Click the "x" to delete it.
2. Delete the app from iTunes.
3. Now reinstall the app. Click "Buy" but don't worry you will not have to pay again as Apple know that you already bought it.
Please note that you will lose any old scores but doing the above does mean that you will be able to play future updates with enhanced features without having to pay for a new version.