Hello!
I had some fields in a SO that I was no longer using so I deleted them. Now, every time I try to run a form that uses this SO, I get the error "Smart Object Unknown could not be found." I can't edit any views or anything either, I check out and then double click to edit and just get a blank area of the screen where the design canvas of the view should be. I get "Object reference not set to an instance of an object" when trying to edit any of the forms. Therefore, I can't even recreate the SO.