[JKT]

It sounds like you may have a corrupted database on your iPhone. If you have a back up of your database on your desktop (i.e. in OmniFocus for the Mac) or on a WebDAV server, to reset the app on your iPhone, delete OmniFocus from your iPhone and re-install it.

You'll have to set-up your preferences again but the imported database from your desktop/back-up should allow you to proceed without the corruption (unless that too is corrupted).