I am hitting a similar problem with gnumeric. Install latest, open
spreadsheet, hit 'safe as' and you get:
(gnumeric:1974): GLib-GIO-ERROR **: Settings schema
'org.gtk.Settings.FileChooser' is not installed
(bit annoying as some work got lost) but easy to reproduce.
This issue suggests a solution:
http://stackoverflow.com/questions/9678301/can-not-use-gtk3-filechooser-on-mac-osx#9684626
i.e., the builder needs to run glib-compile-schemas [path to
org.gtk.Settings.FileChooser.gschema]. There is a compiled schema in
the path, but maybe not for FileChooser and others.