iwidgets::Combobox inherit fails

Another delete class, create.
The code "inherit iwidgets::Combobox" fails with:
cannot inherit from "iwidgets::Combobox" (class "iwidgets::Combobox" not found in context "::iwidgets")


catch {::itcl::delete class iwidgets::ComboBox}

# ComboBox
# ----------------------------------------------------------------------
# additional functionality for iwidgets::combobox

#
# Usual options.
#
itk::usual ComboBox {
        keep -background -borderwidth -cursor -foreground -highlightcolor \
        -highlightthickness -insertbackground -insertborderwidth \
        -insertofftime -insertontime -insertwidth -labelfont -popupcursor \
        -selectbackground -selectborderwidth -selectforeground \
        -textbackground -textfont -index
}

# ------------------------------------------------------------------
#                                                        COMBOBOX
# ------------------------------------------------------------------
itcl::class iwidgets::ComboBox {
        inherit iwidgets::Combobox

        constructor {args} {}
        destructor {}

        itk_option define -balloonhelp balloonHelp BalloonHelp off
        itk_option define -entryballoonhelp entryBalloonHelp BalloonHelp {}
        itk_option define -listballoonhelp listBalloonHelp BalloonHelp {}
        itk_option define -listhelpscript listHelpScript ListHelpScript {}