Created attachment 106791 [details]
Screenshot

The most likely reason is you've got a broken theme installed. That kind of error now simply makes the thumbnailer exit instead of running into an infinite loop. Works for me.

Actually you are right... after removing the Darkgilouche theme everything is working again. I guess this will bite many users, though...

In this case, the problem appears to be that the metacity theme that the metatheme requires is not installed. Therefore, the theme thumbnail cannot be created. However, we should simply skip that theme and still generate thumbnails for all the others. Going to fix this after the end of the code freeze on Monday.

2008-03-11  Jens Granseuer  <jensgr@gmx.net>

        Encountering a theme that could not be thumbnailed (e.g. because the
        metacity theme for a metatheme isn't installed) would make the
        thumbnailer crash. Since it's not restarted by the appearance capplet
        this would result in all themes encountered after the broken one not
        to be thumbnailed either. This change fixes up error handling in the
        thumbnailer so that the broken theme is simply skipped and processing
        can continue with the next one. (bug #521009)

        * theme-thumbnail.c: (create_meta_theme_pixbuf),
        (create_metacity_theme_pixbuf), (message_from_capplet),
        (message_from_child), (read_pixbuf),
        (generate_theme_thumbnail_async), (theme_thumbnail_factory_init):
        properly handle failed thumbnailing attempts