The whole Xfc framework is build with "--prefix=/opt/xfce4", and the $PKG_CONFIG_PATH variable is set to: :/opt/gnome/lib/pkgconfig:/opt/qt/lib/pkgconfig:/opt/xfce4/lib/pkgconfig:/usr/X11R6/lib/pkgconfig. I'm going to be away for the next few days, so the problem has to wait (I guess to Thursday). Thanks in advance.