Getting 'Gtk:ERROR' trying to run WxRuby

I'm using Ubuntu 10.04 and I'm trying to run a WxRuby example which I copy-pasted from this site WxRubyWiki. I've been looking for help over the net but I couldn't find anything similar...

I'm getting this error...

Gtk:ERROR:/build/buildd/gtk+2.0-2.20.1/gtk/gtkwindow.c:6789:IA__gtk_window_present_with_time: assertion failed: (widget->window != NULL)
Aborted

These are the versions I'm using...

ruby -v
ruby 1.8.7 (2010-01-10 patchlevel 249) [i486-linux]
gem list
...
wxruby (2.0.1 x86-linux)
...

And this is the code I'm trying to run...

require 'rubygems' if RUBY_VERSION < '1.9'
require 'wx'

class EventFrame < Wx::Frame
    def initialize()
        super(nil, -1, "Event Frame")
        @idleCounter = 0
        evt_close {|event| on_close(event)}
        evt_idle {|event| on_idle(event)}
        evt_size {|event| on_size(event)}
        evt_key_down {|event| on_key(event)}
        evt_left_down {|event| on_left_down(event)}
        # You can still process these events, you just need to define a separate callback for middle_down and right_down
        # to process them as separate events
        evt_middle_down {|event| on_middle_down(event)}
        evt_right_down {|event| on_right_down(event)}

        button = Wx::Button.new(self, -1, "Push me")
        evt_button(button.get_id()) {|event| on_button(event)}

        show()
    end

    def message(text, title)
        m = Wx::MessageDialog.new(self, text, title, Wx::OK | Wx::ICON_INFORMATION)
        m.show_modal()
    end

    def on_close(event)
        message("This frame will be closed after you push ok", "Close event")
        #close(true) - Don't call this - it will call on_close again, and your application will be caught in an infinite loop
        # Either call event.skip() to allow the Frame to close, or call destroy(), as follows
        destroy()
    end

    def on_idle(event)
        @idleCounter += 1
        if @idleCounter > 15 # Without the counter to slow this down, Idle events would be firing every second
            message("The system is idle right now", "Idle event")
            @idleCounter = 0
        end
        event.request_more() # You must include this, otherwise the Idle event won't occur again
    end

    def on_size(event)
        size = event.get_size()
        x = size.x
        y = size.y
        message("X = " + x.to_s + ", Y = " + y.to_s, "Size event")
    end

    def on_key(event)
        message("Key pressed", "Key Event")
    end

    def on_left_down(event)
        button = ""
        if event.left_down()
            button = "Left"
        end
        message(button + " button was clicked", "Mouse event")
    end

    def on_middle_down(event)
        # This method hasn't been implemented yet...
        #if event.middle_down()
           #button = "Middle"
        #end
        message("Middle button was clicked", "Mouse event")
    end

    def on_right_down(event)
        # This method hasn't been implemented yet...
        #if event.right_down()
            #button = "Right"
        #end
        message("Right button was clicked", "Mouse event")
    end

    def on_button(event)
        message("Button was clicked", "Button event")
    end
end

class MyApp < Wx::App
    def on_init
        EventFrame.new()
    end
end

MyApp.new.main_loop

Thanks in advance!

this fixed and works in ubuntu 11.10 :)