gtk errors "!GTK_WIDGET_REALIZED (widget) failed

[3saul <saul_lethbridge hotmail com>]

when trying to:

GdkColormap *colormap = gdk_screen_get_rgba_colormap(screen);
gtk_widget_set_colormap(widget, colormap);

This is literally as complicated as my program is. Create a window (using
libglade), setup callbacks, apply colormap.

What does this mean? Is there a web page somewhere with an explanation of
such errors?
The full error message is:

Gtk-Critical **: gtk_widget_set_colormap: assertion '!GTK_WIDGET_REALIZED
(widget)' failed
-- 
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