Which version of Ubuntu and of system-config-printer are you using? I have checked and both the versions of system-config-printer currently used by Utopic (14.10) and Vivid (15.04) depend on gir1.2-gtk-3.0.
Is it possible that when you installed gir1.2-gtk-3.0 that an older version of gir1.2-gtk-3.0 got replaced by a newer one? If yes, which was your old version and which the new version of gir1.2-gtk-3.0?
Which version of Ubuntu and of system- config- printer are you using? I have checked and both the versions of system- config- printer currently used by Utopic (14.10) and Vivid (15.04) depend on gir1.2-gtk-3.0.
Is it possible that when you installed gir1.2-gtk-3.0 that an older version of gir1.2-gtk-3.0 got replaced by a newer one? If yes, which was your old version and which the new version of gir1.2-gtk-3.0?