We just found a potential crashing bug in Forest Pack that can happen under these conditions:
Versions: Forest Pack Lite/Pro 3.2.3
Renderer: Mental Ray
Conditions: Rendering objects that have "Custom Edit" mode and "Limit to Visibility" options enabled
How to fix it: Disable "Limit to Visibility" (Camera rollout).
We apologize for the inconveniences, this issue will be fixed in next releases.