For those of you that the mod isn't working all of a sudden. Try to use TPB's steps to clear the .xml file. It can be located in your local appdata>local>Colossal Order>C_S>ForestBrush.xml
Delete that .xml file and reload the game and it should work just fine!

The Mod D:\Gamesnstuff\steamapps\workshop\content\255710\1658679290 [ForestBrush.dll] has caused an error [ModException]

Details:
System.ArgumentOutOfRangeException: Argument is out of range.
Parameter name: index
at System.Collections.Generic.List`1[TreeInfo].get_Item (Int32 index) [0x00000] in <filename unknown>:0
at ForestBrush.ForestBrushTool.CreateBrushPrefab (System.Collections.Generic.List`1 trees) [0x00000] in <filename unknown>:0
at ForestBrush.ForestBrushTool.UpdateTool (System.String brushName) [0x00000] in <filename unknown>:0
at ForestBrush.ForestBrush.Initialize () [0x00000] in <filename unknown>:0
at ForestBrush.UserMod.InstallMod () [0x00000] in <filename unknown>:0
at ForestBrush.UserMod.OnLevelLoaded (LoadMode mode) [0x00000] in <filename unknown>:0
at LoadingWrapper.OnLevelLoaded (UpdateMode mode) [0x00000] in <filename unknown>:0