You can make tiled backgrounds solid by adding the solid behavior - but you usually don't want to do that in top-down games (like the ghost shooter tutorial) - solid means you can't move on top of it!
You don't have to have two layers either, it's just useful for organising your objects (so you can lock the background, for example).
Noesis: you need to tell us what the error messages are, otherwise it's impossible to help. Also, it makes it much easier for us to help you if you share your .capx file. Then we can see what you've actually done. Otherwise we're left guessing!