I didn't realize that copy/paste, undo/redo, and the hollow tools made errors. I have around 100 duplicate planes that are mostly copy/paste houses and hollowed window sills.

I don't notice any adverse effects from the errors and the game works fine. I guess I'm asking can I ignore them or do I really need to go and tear down my house and trench and do it over?

Duplicate planes means two brushes occupy the exact same space..

they can cause glitches, for instance when both of them are differently textured, z-fighting, can occur (two textures "fighting" to be shown)...

It's best to remove them all.

I had alot in one of my maps, and i think it was the cause of some lighting errors.

As for tearing houses down, there is no need.

Open your .map file in notepad, and you can delete the brushes by number. Will save alot of time this way.

But there aren't two brushes occupying the same place because I did the "find brush delete" and it just leaves empty space. Its the window sills i hollowed and they copy pasted to save time. Surely if its a false positive dup plane it doesnt matter?

Strange... I have the same thing in one of my maps... no matter how many times I delete and remake the brush, I get a duplicate plane error... only for one brush though...

Check if you're not filtering anything out... (press "F" and check ALL the boxes).

The_Caretaker writes...

The_Caretaker you made a map???? Where it is???