Hmm, sorry Sapiento, I have no idea why you are getting that error message. Unless somehow the UI enhancements with the Look and Feel have screwed something up, but the program should intercept any such problems and return to the default look if that is the case. So... hmmm. :S
Has anyone else tried it and either got it to work or is getting this error message?
I'll try and tie up a few loose ends on the version I am currently working on and upload it, see if that will get rid of the problem. There will probably be bugs and problems with the feature I am working on but everything else should work ok I guess.
It's great that you have made some brushes for it by the way. I notice that your coloured brushes have some light shading in the actual colouring of the brush. You might want to avoid this if you ever want to mirror the brushes or change the light direction.