On a x64_64 custom live image (with some i686 packages) I ended up with system-config-printer-1.3.7-2.fc16.x86_64 with for example pygobject2-2.28.6-2.fc16.i686 as resolution of the pygobject2 requirement. That didn't work. system-config-printer on x86_64 will use python.x86_64 and it thus can't use the python libraries from pygobject2.i686.

"Fortunately" system-config-printer isn't noarch (because of /lib/udev/udev-configure-printer?) and it could and should use arch specific requires (http://fedoraproject.org/wiki/Packaging:Guidelines#Explicit_Requires ).

As far as I can see the requires section should/could look like this:

Requires: pygtk2%{?_isa} >= 2.12
Requires: pygobject2%{?_isa}
Requires: desktop-file-utils >= 0.2.92
Requires: dbus-x11
Requires: dbus-python%{?_isa}
Requires: system-config-printer-libs = %{version}-%{release}
Requires: gnome-icon-theme
Requires: desktop-notification-daemon
Requires: notify-python%{?_isa}
Requires: gnome-python2-gnomekeyring%{?_isa}
Requires: libxml2-python%{?_isa}
Requires: python-smbc%{?_isa}
Requires: python-slip-gtk