In Ubuntu 11.10, aside from seeing the messages in the terminal periodically, I don't observe any other errors.
In particular, gnome-appearance-properties is no longer available in 11.10, and when using the "Appearance" section of gnome-control-center in the default "Ubuntu" session, no error appears when switching between the Ambiance & Radiance themes (I have not tried in the "Ubuntu 2D" session).
Anyway, it may be hasty to say that the issue is a missing dependency on the gtk2 engine. Perhaps the issue is unpurged legacy content in light-themes. For example, I can grep "pixmap" in /usr/share/themes/Ambiance/gtk-2.0/apps, but nowhere in /usr/share/themes/Ambiance/gtk-3.0/apps.
In Ubuntu 11.10, aside from seeing the messages in the terminal periodically, I don't observe any other errors.
In particular, gnome-appearanc e-properties is no longer available in 11.10, and when using the "Appearance" section of gnome-control- center in the default "Ubuntu" session, no error appears when switching between the Ambiance & Radiance themes (I have not tried in the "Ubuntu 2D" session).
Anyway, it may be hasty to say that the issue is a missing dependency on the gtk2 engine. Perhaps the issue is unpurged legacy content in light-themes. For example, I can grep "pixmap" in /usr/share/ themes/ Ambiance/ gtk-2.0/ apps, but nowhere in /usr/share/ themes/ Ambiance/ gtk-3.0/ apps.