How to solve Gtk-WARNING about “pixmap”

Ubuntu 11.10If you are running Ubuntu 11.10, some applications my generate the following error:

Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap",

How to solve that?

Easy, install gtk2-engines-pixbuf!

From shell you may run:
sudo apt-get install gtk2-engines-pixbuf

Type your password and get it done in few seconds.