Max texture size of the atlas is 4096, size of the atlas is 2048.
I'm on my 3rd rebuild and now it breaks the atlas but also I'm getting a new error from widgets that used to work:
Too many vertices on one panel: 81692
UnityEngine.Debug:LogError(Object)
UIDrawCall:Set(BetterList`1, BetterList`1, BetterList`1, BetterList`1, BetterList`1) (at Assets/NGUI/Scripts/Internal/UIDrawCall.cs:296)
UIPanel:Fill(Material) (at Assets/NGUI/Scripts/UI/UIPanel.cs:941)
UIPanel:LateUpdate() (at Assets/NGUI/Scripts/UI/UIPanel.cs:993)