[Brian]

Hmmm... I'm able to reproduce your symptoms - the keyboard shortcut isn't settable in OmniFocus. If you set it to that shortcut in System Preferences, OmniFocus' preferences show Command-Option-E - but that shortcut doesn't actually work.

I'm going to go ahead and write this up as a bug so the dev team can have a look at the problem, but for the time being you're probably going to need to pick a different shortcut. Thanks for letting us know about the problem, and I'm really sorry for the trouble this is causing.