If you see this error message (Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap"), then try installing "gtk2-engines-pixbuf". If the error appears on a 64-bit system trying to run a 32-bit application, then run these commands (on a Debian-based system as Root).
dpkg --add-architecture i386; apt-get update
apt-get install gtk2-engines-pixbuf:i386