[Lizard]

Can you do me a favor and look for files with "OmniFocus" in their name in any of the folders inside this one on your computer?
<your home folder>/Library/Logs/CrashReporter/MobileDevice

That's where the iPhone crash reports are placed when you sync your phone with iTunes. If you can send along any crash reports you find there, we may be able to determine what's happening and fix the problem.

It would also be helpful to know the following things:
- are you using OmniFocus for iPhone in conjunction with the Mac application or by itself?
- does the application just refuse to start, or do you see a 'loading...' screen for a while before the application shuts down?

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Normally, you can reset the OmniFocus database with the "Reset Database" button in the Settings pane, but it sounds like you're not even getting that far.

You could try backing up and restoring your iPhone through iTunes, but I don't know if that's likely to make a difference.

If you delete the OmniFocus app from your iPhone (press the icon until it wiggles and then tap the X), and then copy it over from iTunes again, it should delete your database and then you can sync it back down from your WebDAV.