If you make a new GUI layer, make sure that 1) the 2d Camera is drawing that layer: "culling mask" 2) the UICamera component is set to send messages to that layer: "Event receiver mask"3) that your whole hierarchy actually uses that layer.4) PhysicsManager should have "Raycasts Hit Triggers"Then it should work fine.
Is your UICamera set to use that layer? Check its event mask.
Yes, it is.Another option?
As I said the #1 reason is that the event mask on the UICamera is not set correctly.