Help:VE189
From TrainzOnline
Collision data exceeds 64KB and has been simplified. Consider using a different generation method or a simplified mesh.
The asset contains complex geometry for which the selected (or default) collision geometry generation technique generated excessively complex results. This would increase memory usage and decrease performance, and as such is prevented by the game- a simplified collision geometry is used instead. This may be harmless, but it also may result in collision detection behaviour from differing from the creator's expectations. Either way, it costs unnecessary performance when installing or validating the asset. The creator should override the collision generation settings for the asset to select a more appropriate method.