When upgrading from Red Hat 5.0 to 5.2 the
$HOME/.gimp/gimprc was replaced with a new one, but was
still pointing to the old brushes/plug-ins etc...(0.99.12-3
Rename or remove the older gimprc and then rerun the gimp app. It
should create a new gimprc with the proper entries for you. The
directoy structure changed with the new gimp version.