I had the same problem but in Mouse Pick simple, in the 3D one, hope it works here too.
At the Layer mask in your Mouse Pick event, modify it to 1 and put a layer over there (doesn't really matter if your app is just at beginning). Go to your BackGround and put the save layer there too (you can modify the layer from "Layer:" near the Tag). On my first, I used Water layer, then I learned how to create one.
I don't really know what you actually want to do but this should work I think.
edit: Before doing that, try to put the OnClick even to the "Mouse Down", not "Mouse Up".