Portal 2 Puzzle Maker/Common Issues
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. Examples of this is creating a block and dragging glass so that in is in the space next to the block but touching the block. The game puts them in at similar point and they will clip in game and the editor can't build it (If you were using hammer and you clipped objects they would work fine. In fact this is how the breakable walls in left 4 dead 2 work.) to fix it just simply move the glass so it doesn't touch any blocks.