Hi,
Forest creates a "forest_templates" layer to store there all distributed and templates objects and by default all objects inside this layer are hidden and frozen.
Might be, you've moved that Forest object into this layer? As these objects can be manipulated like any other 3ds max's object (moved to other layer, copied etc.), by moving it under any other layer (like the 0 (default)) should fix it.
Hope that helps.
Best regards,