The red triangle unfortunately for now is a catch all for various rules that mean you can't fit that module on your ship. So the total mass of your ship can't exceed the drive max mass it can support. You can't fit a shield gen that has a max mass smaller than the ships Hull Mass (though granted we don't tell you what the hull mass is, but it's roughly less than half the mass of a typical loadout). There are other rules but they're pretty minor like not being to sell life support and go without kind of thing. This will be improved in time. The outfitting is still very work in progress.