removeChild() problem

1

My day 3 of AS3 and i found no go beyond this problem:
[COLOR=#0000cd]
[/COLOR]when i press MyMenu1 it loaded the sub menu correctly, when i press it twice i got this error

TypeError: Error #2007: Parameter child must be non-null.
at flash.display::DisplayObjectContainer/removeChild()
at MunibaseCalculator_fla::MainTimeline/MyMenu1_Clicked()

what i m trying to do is, load the MC when MainMenu is pressed and unload it when i pressed it again.

Any help verry much appreciated.
[COLOR=#0000cd]

var[/COLOR] MyMenu1:MainMenu_btn1 = [COLOR=#0000cd]new[/COLOR] MainMenu_btn1();
MyMenu1[COLOR=#ff0000].x[/COLOR] = 80;
MyMenu1[COLOR=#ff0000].y[/COLOR] = 85;
[COLOR=#ff0000]addChild/COLOR;

[COLOR=#0000cd]var[/COLOR] MyMenu1_Logic[COLOR=#ff0000]:Boolean[/COLOR] = [COLOR=#ff0000]false[/COLOR];
MyMenu1.[COLOR=#ff0000]addEventListener[/COLOR]([COLOR=#ff0000]MouseEvent.CLICK[/COLOR], MyMenu1_Clicked);
[COLOR=#0000cd]function[/COLOR] MyMenu1_Clicked([COLOR=#ff0000]event:MouseEvent[/COLOR])
{
trace([COLOR=#00ff00]“Main Menu Pressed”[/COLOR]);
[COLOR=#0000cd]if[/COLOR] (MyMenu1_Logic ==[COLOR=#ff0000] false[/COLOR])
{
[COLOR=#0000cd]var[/COLOR] MyMainMenu:MainMenu = [COLOR=#0000cd]new[/COLOR] MainMenu();
MyMainMenu[COLOR=#ff0000].x[/COLOR] = 0;
MyMainMenu[COLOR=#ff0000].y[/COLOR] = 105;
[COLOR=#ff0000]addChild/COLOR;
MyMenu1_Logic = [COLOR=#ff0000]true[/COLOR];
[COLOR=#ff0000]trace[/COLOR]([COLOR=#00ff00]“Sub Menu Loaded”[/COLOR]);
}
[COLOR=#0000cd]else if[/COLOR] (MyMenu1_Logic == [COLOR=#ff0000]true[/COLOR])
{
[COLOR=#ff0000]removeChild/COLOR;
MyMenu1_Logic = [COLOR=#ff0000]false[/COLOR];
[COLOR=#ff0000]trace[/COLOR]([COLOR=#00ff00]“Sub Menu Unloaded”[/COLOR]);
}
}