Your scene uses objects created with Forest 2. Because of significant differences between versions, Forest 3 doesn't handle the objects created with Forest 2, although you can have both versions installed simultaneously.
You can download from User Panel->Previous versions the latest Forest 2 release so you can to open old scenes. However, this version of the plugin is supported only to 2009.
I've also attached a maxscript file to convert Forest 2 objects to Forest 3. These scripts are unfinished and don't handle all existing parameters, but would help you for upgrading your scenes.