Forum attachments have been disabled for several years now. You can thank the people that abused them for them being disabled.
As for your problem, see this
. The colored boxes you see represent how big a monster can be inside it. Any bigger than the box, and you'll get the errors your screenshot shows. Unfortunately, the moulds are kind of limiting, so you'll have to work with what you have.
Yes, you could add more or tweak pre-existing moulds, but that's a rather involving process.