Last week I had an hour to fly finally but for the first time since I have had the Iris+ I could not engage the copter with the controller. I was able to engage it with my phone using the antenna and App, then the controller worked to fly the copter and even to disengage once I landed. I did just a little research and didnt find a solution but was hoping there was a quick fix some one could relay to me 
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Very little information here. Any number of things could cause this. The most likely is you had the mode switches in the wrong place.
You should have had some lights and sounds on the copter that would indicate the issue.
You should start with all the switches flipped away from you.
Mike
I have a similar problem.
Sometimes I cannot arm the iris+ from the Iris+ transmitter. But I can from the tablet app.
After the drone is armed, I have no problems, except I cannot disarm the drone from the Transmitter. Again the app works fine.
What I have found, is that if I adjust the trim tab on the transmitter as far down as I can, then the drone arms and disarms from the transmitter. On occasion I also have to pull the trim all the way to the left or right to get the arming/disarming to work correctly.
Does anyone know if this can be adjusted in the Iris+ software to be a little more forgiving?
I am a relative noob but it sounds to me like it isn’t seeing the throttle arming signal in the full down-and-right position unless you go even farther that way with the trim. So I think you might need to calibrate the transmitter sticks so that it produces the full range signal when you take the stick there. It is an easy procedure. Make sure to have the trims centered before doing the cal.
I agree with the above. And I have read that the trims must ALL be centered, for the Pixhawk to perform properly. 
Check and make sure that the sticks are calibrated correctly. youtu.be/m73ApapSDzc
If the throttle stick is not centered properly it will not create the correct value when you move it to arm/disarm the motors.
ToddH.