I've had a quick play and find that changing the foundation to Monlithic Slab solves the problem with all the walls. As the foundation type is not critcal to this project I'll just leave it set to that. Thanks for your hepl.
I hope somebody can help with my problem. You can see from the attached that my walls and floors don't line up and I have a bit of roof at the bottom of my 1st floor wall. Can anybody explain what is going on?