Hi Colin,
You are upgrading to 2.2.2.8 right?
I'm not entirely sure whats going on with thast error. I actually got that error myself when I upgraded joeaudette.com. It could be that not all the files got deployed? For me it fixed itself when I copied the files up again.
You might also try deleting your cookies. The name of the role cookie has changed in recent versions, I would not think this would cause an error but you never know.
Hope it helps,
Joe