Large puzzles with many items may result in a 'too many items' error. If this doesn't work, you can try uninstalling the Portal 2 Authoring Tools. It will then download any broken or missing files. Do this by opening Steam and right-clicking on Portal 2 Authoring Tools, then select Properties > Local Files > Verify Integrity of Tool Cache. If you have Portal 2 Authoring Tools installed, verify the game files. If an enabled funnel is pointed at the entrance way, it will come through the 2nd entrance door.When an open door is reflected in goo, you can see the 2 sides of the door that go into the wall (You are not suppose to see when the door is open).The map you are working on in the editor may disappear completely, sometimes from zooming in/out and will not come back.To fix this just remove some items on your map. If when you try to build your level you get an error that says unable to build level it is most likely you have created something the editor can't render.
