Reproducible Crash report - surface areas & undo

[SnipeyX]

Max Design 2015 SP2.
ForestPro 4.2.5.
New Scene.
Create a plane primitive.
Create a ForestPro object by clicking on the plane.
Delete the plane.
Undo.
Crash.
 

[iToo]

Thanks for reporting the problem, we can reproduce it.
We'll fix it for the next Forest update. I apologize for the inconvenience.