Hi, could you please provide more information about what the error message says?
Also, I would like to suggest that you try using the Corona Renderer 10 daily build version, as it contains several bug fixes related to using Forest Pack in the scene. It is possible that the issue you are facing has been resolved in this version.
https://forum.corona-renderer.com/ Chaos Corona 10 for 3ds Max - Daily Builds Changelog
If you are willing to try the daily build version, we would appreciate it if you could provide us with feedback on whether the issue persists or not.
Note: The daily builds are the newest, experimental versions of Corona Renderer intended mainly for testing purposes and to showcase the recently added features. They contain the latest bug fixes but are not guaranteed to be stable, and in some cases can even damage scene files.
Check this link to know more about it: https://support.chaos.com/hc/en-us/articles/4528206493329-Corona-for-3ds-Max-Daily-Builds-