If it's a subscript error that definitely points to either too many vertices on the freeform line or too many vegetation boxes. I don't have error handling written for those areas yet. In the latest version I've upped the number of vegetation squares that can be created so it'll probably take care of that problem. Would be simple code though to say "don't create the square or the vertice if you're at the maximum number of array elements". Sometimes I'm a lazy programmer. This is one of them.
I am working on "improving" the photographic Georender.com Cinematic Alaska. This is an 11000sqkm area near Anchorage Alaska. There is some autogen but it can use more, especially trees. This is where the freeform tool really works well. The generation of multiple tree "boxes" to fill a small area is an advantage when maximizing the tree density. Very effective and time saving. The scenery package has 14264 textures so I have a few more ahead of me!!