I’m newbie
After few days of using Iris I install 3.1.4quad firmware. And Iris don’t arm after that 
Try different modes. I know it must start in stab mode, but don’t. Confused whats problem it can be 
You remembered enable the safety switch (press and hold), right?
connect your iris to your computer and open up mission planner, see if there are any error messages, during pre arm there are a series of checks and if one fails it will give you a message on the HUD.
Sorry for late reply but the same day problem solved.
Don’t know why but after firmware 3.1.4 upgrade through APM planner problem was gone.
Yesterday updated to 3.1.5 trough mission planner and no problem.
Thanks all