Comment #5 on issue 649 by tu...@tudorgirba.com: PNG, BMP, GIF exports do not work anymore in Mondrian http://code.google.com/p/moose-technology/issues/detail?id=649
Before you do that, there should be only one dialog, not two. Right now, first you ask for the file name and then for the folder. But, you can use one dialog to get the file and folder:
UITheme builder fileSave: 'Your title here' extensions: #('png') path: nil.