So, did you get this error also working with other scenes, not only the grass tutorial ?
It seems there is some file corrupted in Max (because the "File Open Error" title of the error dialog), probably something related with the materials.
If you are worried about whether Forest Lite is triggering this error, i would suggest uninstall the plugin temporary and see if the problem remains. Sincerely, seeing the symptoms, i think this error is not caused directly by Forest. Similar issues have not been reported by other users either.