Sorry about the expired license! This only affects users who downloaded OmniFocus on the very first day, back when you had to enter a license by hand to be able to use OmniFocus. That hand-entered license is overriding the one we now build into the application, so the solution is to delete it:
- At the "This license is not licensed" prompt, click "Add License".
- On the license screen that follows, select the expired license and click "Delete License".
- When prompted to confirm that you want to delete the expired license, click "Delete".
- Quit and relaunch OmniFocus, and you should be licensed.
Again, I'm sorry for the inconvenience!