I'm also running this application on a 10.5.8 desktop iMac. I know how to create a brush (create image, have a transparent background, convert to "
Grayscale," save with gbr {am I forgetting anything}) but the grayscale part is what's not working. I convert the image to grayscale, but when I "Save As" and ad ".gbr" at the end of the title, I get this error message; apparently I can't save ...