Element 3D layer is not visible in 3d scene

If you are trying to load an element 3D scene into a camera tracked scene you need to Normalize the comp. That means you need to set an origin and ground plane, realize that the origin and ground plane are centered at 0, 0, 0. Add some reference solids to the scene, add another 3D null to the scene and name it Normalize, then put the normalize null at 0, 0, 0, parent all the reference 3D solids (I don't use nulls because you can't see if they are tracking when you preview), the camera, and any other 3D layers to the Normalize Null, then reset the position of the Normalize Null to comp center. If you do this then the Element 3D comp center will now match with the Camera. When all that is done, oh, and by the way, it needs to be done on the frame you used to set the origin and ground plane, you can at least see where the object element created is in the scene. 

Once you are there you then have to create a null using Element 3D to control the 3D position of the object in AE's world. Select Group 1, Spin down the options and create a null to control group 1. When the null is created you can hold down the Shift Key and parent the controller null to the reference solid you have in the scene that matches where you want the object from Element to end up.

This will work without Normalizing the comp first, but your 3D world can end up being really crazy and it makes it really hard to add other 3D elements to the scene. There are some tutorials over at Video Copilot that explain exactly how to do this. There is also a "pay what you can" or maybe even free script somewhere that automates the Normalize Comp workflow.