Hey there @alehandrof! Sorry for the trouble here.
Is there any chance OmniFocus is performing a sync while the archive sheet is up? If you wait a little while, does the button become available on its own?
I don’t think it was syncing at the time. I tried it again now and the button is disabled (and it’s not syncing). It doesn’t seem to go away on its own, unless I restart the app.
That’s strange! If you haven’t already, would you mind sending in an email to support? This might be a bug in OmniFocus, and support can help make sure it’s reported properly.
Thanks for mentioning this problem. It’s reports like this that help us continue to improve OmniFocus.