Gah! I think I have worked out why it isn't working. Tsk. This goes to show that although 0.75 has been downloaded 10 times so far, no-one is giving me feedback. So thanks for that Sapiento.
As a quick fix, without the need for me to upload a new version, here is a missing directory that should have been included with the previous version.
This needs unzipping into the TreeThing root directory, so you should be able to see the directory in the same place as the brush directories.
Sorry about that.