UPDATE: The problem has been identified. Follow this link to get your database opening again and to learn more about what's causing the problem.
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Since the 1.6.2 version went up on the app store, we've received reports of folks getting stuck and crashing during the "Optimizing Database" stage. We're really sorry for the inconvenience these crashes are causing!
We haven't been able to reproduce the problem on any of our test devices, but the information we've gathered so far seems to indicate that the problem is in some way time-related.
In order to determine exactly what's wrong and fix the issue, it would be tremendously helpful to sync the crashing device with iTunes, then look for files with "OmniFocus" in their name in any folders inside in these locations one on the computer:
On a Mac: <your home folder>/Library/Logs/Crash Reporter/MobileDevice
On a Windows computer: C:\Documents and Settings\<your user name>\Application Data\Apple Computers\Logs\CrashReporter\MobileDevice
(That's where the iPhone crash reports are placed when you sync your phone with iTunes.)
Sending along any OmniFocus crash reports you find there to the
Support Ninjas will help tremendously in determining exactly what's happening so we can get this fixed.
Again, we're very, very sorry for the trouble this is causing!