What is this plane?

What seems to be a plane through the origin has started to show up in my file. See the image. It is grey and when viewed from the top cuts my model in half with the bottom half not visible but the top half is. If I rotate the view to below the horizon the plane goes away and everything is visible.Image%201

Hello - this looks like the ground plane - open the GroundPlane panel (Panels menu) and set it to Automatic (will always be the floor for the lowest object) or turn it off…
Any luck?

-Pascal

Yes that worked, I turned it off. Wonder how it got turned on?