

Moderator: Core Staff
So since there's so many of them and it doesn't seem to cause any noticable problems, remaking all those brushes just isn't worth it. But you might want to pay attention to errors like that during each compile in future maps, and fix them as they appear.This error means you have two faces on a brush that are in the same plane, meaning one brush has a single face composed of 2 faces. You will need to find, delete and recreate the brush (this error could be left alone without any major problem for MP maps).
When you were editing a brushes vertices, at some point you dragged the vertices in such a way that the two planes opposite each other were in the same place. While this error isn't necessarily a vital problem in the compile process, it can cause some weird visual side effects as you basically have a double-sided texture. It is generally best to avoid this, but it is technically okay to leave it as it is.