Hmm, that is_guest_ordershould have been added to the orders' table on an install/upgrade to v2.0.0 (or later). If that's not there, there's also the possibility that other database configuration items weren't added either.
@shags38, would you post a screenshot of your store's Configuration->One-Page Checkout Settings for review?
Hi Cindy - configuration settings below as requested - v2.0.4 settings were exactly the same
cheers,
Mike Attachment 17989