Once the owner of the Resource has been migrated you can no longer modify the Resource until it too is migrated to Exchange.
The Mail System field of the Person document of the Owner was changed from Notes to Other Internet Mail. This makes the Resource believe that the owner no longer exsists in Domino. When you go to modify the Resource it will not let you save changes until you deal with the owner no longer in domino.
Change the person document of the owner back from "other internet mail" to "Notes" Replicate the change, modify the Resource then change the owner's Doc back to "other internet mail".